Haiti, a nation rocked by gang cruelty and plagued with political infighting, has — so far this year — had three prime ministers, seen at least 4,000 people killed and experienced brutality from armed groups so intense that it forced an extended closure of its international airport, twice.

But despite $600 million spent by Washington on an international police force to restore order, an explosion of violence last week underscored the enormity of a crisis so severe that the Federal Aviation Administration has barred U.S. aircraft from flying under 10,000 feet in Haitian airspace to avoid being shot at by gangs.

With another interim prime minister in place, but gangs gaining territory every day, Haitians are desperate for relief. Efforts to stabilize Haiti are floundering, and the country presents a dangerous and disastrous challenge as President-elect Donald J. Trump prepares to take office.

Few people seem to have answers.

“I am at a complete loss,” said Susan D. Page, a University of Michigan Law professor and former United Nations official in Haiti. “Everyone is just kind of astounded.”

What’s going on?

Haiti has experienced a long-simmering crisis for about 15 years, a period marked by a devastating earthquake, squandered aid dollars, tarnished international interventions and flawed presidential elections.

In 2021, the president, Jovenel Moïse, was assassinated in his house. The United States played a hand in deciding who would become the next prime minister, but many Haitians opposed the choice, Ariel Henry. During his three-year tenure, killings and kidnappings by well-armed gangs surged.

The United States had little appetite for sending its own troops to take on the criminal groups. Instead, the Biden administration devised a plan for an international mission made up mostly of Kenyan police officers to help support the local police.

In February, while Mr. Henry was in Kenya finalizing the plan’s details, rival gangs in Haiti banded together, unleashed terror and forced him out.

For months, the main airport was closed, neighborhoods were burned and civilians were killed. To fill the power vacuum, the United States and Caribbean countries helped Haiti hatch a plan for a nine-member transitional presidential council to rule the country.

A former U.N. official, Garry Conille, was named interim prime minister. The Kenyans arrived in June and gangs appeared, at least briefly, to pull back.

What’s happening now?

The presidential council announced last week that it had fired Mr. Conille and replaced him.

In an apparent effort to sow mayhem and demonstrate that they still wield considerable power, gang leaders escalated their attacks. They shot at least three U.S. aircraft on Monday and took over more neighborhoods in Port-au-Prince, the capital.

Videos circulated on social media showed people running through streets, many lugging children and suitcases.

An already grim situation could get worse. Gangs have traditionally steered clear of upper-class neighborhoods where wealthy Haitians, diplomats and international humanitarian aid workers live. But experts fear that could soon change, leaving the entire capital in the hands of armed groups that some are now calling “paramilitaries.”

So what now?

The Kenyan-led mission the Biden administration created and funded is widely viewed as a disappointment. Few other countries contributed money, leaving the force with less than 400 police officers, far less than the 2,500 initially envisioned.

Mr. Trump has made disparaging comments about Haiti, and many people think he will make the Kenyans leave as soon as he takes office. (His team did not respond to a request for comment.)

The Biden administration is pushing hard for the Kenya police mission — known as the Multinational Security Support mission, or M.S.S. — to be converted into an official U.N. peace keeping force. That would solve several problems: a lack of personnel, equipment and money. A U.N. peace keeping force would obligate member nations to contribute financially and provide troops, taking the burden of finding money and officers out of Washington’s hands.

Even though the last U.N. peacekeeping force brought cholera to the country and was embroiled in sexual abuse scandals, the current situation is so desperate that the move would largely be welcomed.

But China and Russia, which have veto power, have made clear that they’re not interested in such a move. The U.N. Security Council is expected to discuss sending an assessment team to Haiti to explore the idea this week, said a senior U.S. official who was not authorized to publicly discuss Haiti policy.

The hope is that the two countries will abstain instead of vetoing the proposal, according to several officials familiar with the talks.

Still, even if a U.N. peacekeeping mission were approved, it would take months to create, the U.S. official said.

The current multinational force is expected to increase to 1,000 officers by the end of the year with the addition of air support from El Salvador and marine support from the Bahamas, the official said. Haiti will also soon get about 20 more armored vehicles.

The mission was hampered because countries in the Caribbean and Latin America with a direct interest in preventing a mass migration out of Haiti did not provide the help they should have, the official said.

President Biden discussed a U.N. peacekeeping force with President Xi Jinping of China during their meeting at the Asia-Pacific Economic Cooperation forum in Peru on Saturday, but the Chinese leader did not change his mind, national security advisor Jake Sullivan.

If the U.N. Security Council rejects the move, another option would be to beef up the multinational mission. But Congress has balked at spending more money for Haiti.

Pressed on whether the Biden administration’s strategy was failing, a second senior U.S. official said the administration had done what it could with the limited resources Congress made available, adding that lawmakers were not treating the crisis in Haiti with the same urgency as other emergencies across the globe, like Ukraine or the Middle East.

The official, who spoke on the condition of anonymity to discuss diplomatic plans, maintained that the United States has kept the Haitian government from collapsing.

Will negotiating with gangs be necessary?

Vanda Felbab-Brown, an expert on nonstate armed groups at the Brookings Institution, said that if the crisis persists, it will likely force the Haitian government to make an unpalatable, but perhaps necessary move.

“If desperation reaches epic proportions, I think a more likely scenario is to see the political system” negotiate with the gangs, she said, adding that “would give gangs more power than they have already.”

That’s easier said than done. There are up to 20 different gangs operating in Port-au-Prince, and many of them have committed horrific crimes. While gang leaders talk openly about wanting a “seat at the table,” they have not offered to lay down their weapons, and the Haitian government is determined not to negotiate from a position of weakness, several experts said.

Nobody is seriously discussing amnesty for gang leaders who have committed multiple homicides. But with gangs having an estimated 12,000 members — half of them minors — serious talks would eventually have to take place to figure out how to disarm, demobilize and reintegrate them into society, the first U.S. official said.

Many gang members are desperately poor teenagers who lack job opportunities. Analysts agree that the Haiti needs to implement significant job training and educational programs to lure children from the grips of armed groups that pay a regular salary.

Talks are unlikely to start until the M.S.S. and the Haitian National Police succeed in capturing or killing top leaders, a goal that they have yet to achieve.

Stemming the flow of guns

Several Haiti experts stressed that the United States needs to do more to end the flow of guns from its shores to Haiti. Whether the solution is a full arms embargo or tougher sanctions on people known to finance and control gangs, experts agreed that the crisis will not end until high-powered weapons are off the streets.

“This is what Haitians have been consistently saying: ‘We do not produce guns,’” said Nathalie Frédéric Pierre, a Haiti expert at Howard University. “This is what is choking our society.”

Several Haitians interviewed expressed disappointment that the United States had spent so much money on the international force rather spending more on the Haitian National Police, which is vastly understaffed and ill-equipped.

“We wasted a lot of time money and energy that could have been invested in to our own Haitian solution,” said Vélina Élysée Charlier, a human-rights activist in Port-au-Prince.

Leslie Voltaire, who is currently president of the transitional presidential council — a position that rotates every few months — said he hopes to see the police accomplish a few victories against the gangs, even if it’s against “low-hanging fruit.”

“We are seeing that the international community is helping, but in a very slow way,” he said.

He hopes to see the Kenya mission reinforced with a better flow of supplies.

He said he is working on an action plan to submit to the international community that includes constitutional reform and planning for presidential elections next November.

“This is our road map, but it is very bumpy,” he said.

He does not know whether Mr. Trump will end the Kenya-led mission.

“I sent a tweet to him saying congratulations,” Mr. Voltaire said. “I know he loves tweets.”

He hasn’t heard back.

Zolan Kanno-Youngs, David C. Adams and André Paultre contributed reporting.

President Biden has authorized the first use of U.S.-supplied long-range missiles by Ukraine for strikes inside Russia, U.S. officials said.

The weapons are likely to be initially employed against Russian and North Korean troops in defense of Ukrainian forces in the Kursk region of western Russia, the officials said.

Mr. Biden’s decision is a major change in U.S. policy. The choice has divided his advisers, and his shift comes two months before President-elect Donald J. Trump takes office, having vowed to limit further support for Ukraine.

Allowing the Ukrainians to use the long-range missiles, known as the Army Tactical Missile Systems, or ATACMS, came in response to Russia’s surprise decision to bring North Korean troops into the fight, officials said.

President Volodymyr Zelensky of Ukraine did not confirm the permission to strike but suggested on Sunday that more important than lifting the restrictions would be the number of missiles used to strike the Russians.

“Today, many in the media are talking about the fact that we have received permission to take appropriate actions,” Mr. Zelensky said in his nightly address. “But blows are not inflicted with words. Such things are not announced. The rockets will speak for themselves.”

Mr. Biden began to ease restrictions on the use of U.S.-supplied weapons on Russian soil after Russia launched a cross-border assault in May in the direction of Kharkiv, Ukraine’s second-largest city.

To help the Ukrainians defend Kharkiv, Mr. Biden allowed them to use the High Mobility Artillery Rocket System, or HIMARS, which have a range of about 50 miles, against Russian forces directly across the border. But Mr. Biden did not allow the Ukrainians to use longer-range ATACMS, which have a range of about 190 miles, in defense of Kharkiv.

While the officials said they do not expect the shift to fundamentally alter the course of the war, one of the goals of the policy change, they said, is to send a message to the North Koreans that their forces are vulnerable and that they should not send more of them.

The officials said that while the Ukrainians were likely to use the missiles first against Russian and North Korean troops that threaten Ukrainian forces in Kursk, Mr. Biden could authorize them to use the weapons elsewhere.

Some U.S. officials said they feared that Ukraine’s use of the missiles across the border could prompt President Vladimir V. Putin of Russia to retaliate with force against the United States and its coalition partners.

But other U.S. officials said they thought those fears were overblown.

The Russian military is launching a major assault by an estimated 50,000 soldiers, including North Korean troops, on dug-in Ukrainian positions in Kursk with the goal of retaking all of the Russian territory that the Ukrainians seized in August.

The Ukrainians could use the ATACMS missiles to strike Russian and North Korean troop concentrations, key pieces of military equipment, logistics nodes, ammunition depots and supply lines deep inside Russia.

Doing so could help the Ukrainians blunt the effectiveness of the Russian-North Korean assault.

Whether to arm Ukraine with long-range ATACMS has been an especially sensitive subject since Russia’s full-scale invasion of Ukraine in February 2022.

Some Pentagon officials opposed giving them to the Ukrainians because they said the U.S. Army had limited supplies. Some White House officials feared that Mr. Putin would widen the war if they gave the missiles to the Ukrainians.

Supporters of a more aggressive posture toward Moscow say Mr. Biden and his advisers have been too easily intimidated by Mr. Putin’s hostile rhetoric, and they say that the administration’s incremental approach to arming the Ukrainians has disadvantaged them on the battlefield.

Proponents of Mr. Biden’s approach say that it had largely been successful at averting a violent Russian response.

Allowing long-range strikes on Russian territory using American missiles could change that equation.

In August, the Ukrainians launched their own cross-border assault into the Kursk region, where they seized a swath of Russian territory.

Since then, U.S. officials have become increasingly concerned about the state of the Ukrainian army, which has been stretched thin by simultaneous Russian assaults in the east, Kharkiv and now Kursk.

The introduction of more than 10,000 North Korean troops and Mr. Biden’s response come as Mr. Trump prepares to re-enter office with a stated goal of quickly ending the war.

Mr. Trump has said little about how he would settle the conflict. But Vice President-elect JD Vance has outlined a plan that would allow the Russians to keep the Ukrainian territory that their forces have seized.

The Ukrainians hope that they would be able to trade any Russian territory they hold in Kursk for Ukrainian territory held by Russia in any future negotiations.

If the Russian assault on Ukrainian forces in Kursk succeeds, Kyiv could end up having little to no Russian territory to offer Moscow in a trade.

Mr. Zelensky has long sought permission from the United States and its coalition partners to use long-range missiles to strike Russian soil.

The British and French militaries have given the Ukrainians a limited number of Storm Shadow and SCALP missiles, which have a range of about 155 miles, less than the American missile system.

While British and French leaders voiced support for Mr. Zelensky’s request, they were reluctant to allow the Ukrainians to start using their missiles on Russian soil unless Mr. Biden agreed to allow the Ukrainians to do the same with ATACMS.

Mr. Biden was more risk-averse than his British and French counterparts, and his top advisers were divided on how to proceed. On Sunday, some Republican lawmakers praised the move but said it had come too late.

“For months I have called on President Biden to remove these restrictions,” Representative Michael R. Turner of Ohio, the chairman of the House Intelligence Committee, said in a statement. ”President Biden should have listened to President Zelensky’s pleas much earlier.”

Some of Mr. Biden’s advisers had seized on a recent U.S. intelligence assessment that warned that Mr. Putin could respond to the use of long-range ATACMS on Russian soil by directing the Russian military or its spy agencies to retaliate, potentially with lethal force, against the United States and its European allies.

The assessment warned of several possible Russian responses that included stepped-up acts of arson and sabotage targeting facilities in Europe, as well as potentially lethal attacks on U.S. and European military bases.

Officials said Mr. Biden was persuaded to make the change in part by the sheer audacity of Russia’s decision to throw North Korean troops at Ukrainian lines.

He was also swayed, they said, by concerns that the Russian assault force would be able to overwhelm Ukrainian troops in Kursk if they were not allowed to defend themselves with long-range weapons.

U.S. officials said they do not believe that the decision will change the course of the war.

But they said Mr. Biden determined that the potential benefits — Ukraine will be able to reach certain high-value targets that it would not otherwise be able to, and the United States will be able to send a message to North Korea that it will pay a significant price for its involvement — outweighed the escalation risks.

Mr. Biden faced a similar dilemma a year ago when U.S. intelligence agencies learned that the North Koreans would supply Russia with long-range ballistic missiles.

In that case, Mr. Biden agreed to supply several hundred long-range ATACMS to the Ukrainians for use on Ukraine’s sovereign territory, including the Russian-occupied Crimean Peninsula. Those supplemented the more limited supplies of Storm Shadow and SCALP missiles that the Ukrainians received from Britain and France.

The Ukrainians have since used many of those missiles in a concerted campaign of strikes against Russian military targets in Crimea and in the Black Sea.

As a result, it is unclear how many of the missiles the Ukrainians have left in their arsenal to use in the Kursk region.

Two waves of Israeli airstrikes hit Lebanon’s capital on Sunday, rare attacks inside Beirut that come as Israel’s military has been pounding areas outside the city where Hezbollah holds sway.

Israel’s intensified push appears aimed at pressuring the Lebanese government and Hezbollah to accede to terms for a cease-fire for Lebanon worked out between Israeli and American officials, in what Israeli analysts describe as a strategy of “negotiations under fire.”

Lebanon’s Health Ministry said at least six people were killed in Sunday’s strikes in Beirut, the first to hit the city in weeks. The attacks rattled residents, reviving fears that the city could be consumed by the larger war.

The infrequent strikes inside the capital have tended to target individuals belonging to Hezbollah. On Sunday, the first attack killed Mohammed Afif, the head of Hezbollah’s media office, according to Hezbollah and the Israeli military.

As the de facto spokesman of Hezbollah, Mr. Afif was one of the group’s few remaining figures with a public profile. His role had gained more prominence in recent weeks after Israel killed Hezbollah’s leader, Hassan Nasrallah, in September along with much of the group’s top command and leadership.

The Israeli military said late on Sunday that it had killed Mr. Afif in a “precise, intelligence-based strike,” calling him Hezbollah’s chief spokesman and saying he was “directly involved in advancing and executing Hezbollah’s terrorist activities against Israel.”

On Sunday evening, the Israeli military again struck in Beirut in the area of Mar Elias, according to Lebanon’s Health Ministry, which said that at least two people were killed and 22 wounded in the strike. The attack ignited a large fire in the building that was hit, sending plumes of smoke billowing into the neighborhood. There was no immediate comment from Israel’s military about the second strike.

The strike in Beirut earlier on Sunday destroyed a seven-story building in the neighborhood of Ras al-Naba, Lebanon’s state-run news agency reported. It said that search teams were working to rescue a number of people trapped under the rubble and that Mr. Afif was “coincidentally present” when the building was struck. The Lebanese Health Ministry said on Sunday that four people were killed in the attack on Ras al-Naba.

The building housed the Lebanese headquarters of the Arab Socialist Baath party, a small political faction aligned with Hezbollah. In a statement, the party said that its leader, Ali Hijazi, was not in the building at the time of the strike.

The explosion set off panic and confusion in the city. People rushed out into the street, some screaming, others trying to reach people by phone. Smoke and dust filled the air and gunfire rang out as multiple ambulances rushed to the scene, where a crowd had gathered.

Um Ahmad, who gave only her first name, stood across from the building, her three young daughters huddled behind her. She said that she, her husband and their six children were staying in a nearby apartment along with dozens of others displaced by the war. The moment they heard the blast, they rushed out of their building in fear.

“We heard a loud boom and left immediately,” she said.

Earlier Sunday, the Israeli military said it had conducted “intelligence-based strikes” against Hezbollah on the Dahiya, an area just south of Beirut where the militant group holds sway. A spokesman for the Israeli military, Avichay Adraee, said on Sunday that Israel had struck 50 targets in the area over the past week.

Abu Hussein had fled the Dahiya and taken a job as a security guard at a building in Beirut a few weeks ago. The building where he works was the one that was hit first on Sunday.

After the strike, Mr. Hussein stood nearby in a daze. His head bandaged, and streaks of blood ran down his neck.

“The building was nearly empty” when the strike hit, Mr. Hussein said, as medics tended to his wounds.

Mr. Afif had appeared in public in recent weeks to speak to reporters at news conferences in the Dahiya. During one news conference last month, Mr. Afif told reporters that Hezbollah had taken responsibility for an aerial attack that targeted the home of Israel’s prime minister, Benjamin Netanyahu. When Israeli warnings of an imminent strike sent journalists scrambling to gather their equipment and leave, Mr. Afif told them, “The bombardments don’t scare us, so how should the threats scare us?”

A week ago, Mr. Afif said at a news conference that Hezbollah had not yet received any official proposal for a cease-fire deal — though he noted that there had been “contacts between Washington, Moscow, Tehran and other capitals” on the issue since the election of former President Donald J. Trump.

Hezbollah, he cautioned, remained “ready for a long war.”

Israel began an intensified military campaign against Hezbollah in September, nearly a year after the group began firing rockets into Israel in solidarity with Hamas in Gaza. The offensive set off a humanitarian crisis in Lebanon, displacing nearly a quarter of the population and buckling the country’s health system.

Lebanon’s Health Ministry said on Sunday that Israeli attacks had killed 29 people on Saturday, bringing the death toll since the fighting between Israel and Hezbollah began in October 2023 to more than 3,480 people. The ministry does not distinguish between civilians and combatants.

The campaign against Hezbollah initially focused on southern Lebanon, where Israel’s military said it sought to stop the group from being able to fire rockets across the border. But the military operations have expanded in recent weeks to include cities and towns across the country, including some far from that border. And Hezbollah has maintained its ability to launch rockets into Israel.

The Israeli military said on Sunday that about 35 rockets were fired into the country from Lebanon, setting off alert sirens in the area around Haifa, Israel’s main northern port city, and other places. Some of the rockets were intercepted by Israel’s air defenses, and others fell in open areas. One person was moderately injured, according to Israel’s emergency medical services.

Christina Goldbaum contributed reporting from Beirut, and Gabby Sobelman from Rohovot, Israel. Ephrat Livni also contributed reporting.

An Israeli judge on Sunday revealed more details in a case involving an official in Prime Minister Benjamin Netanyahu’s office and a military officer suspected of leaking and mishandling classified intelligence documents — an accusation that has been roiling the country in the midst of war.

The judge said in his ruling that the leak was intended to influence Israeli public opinion in a way that would reduce popular pressure on Mr. Netanyahu to reach a deal to secure the release of hostages and end the war in Gaza.

State prosecutors also asked the court to extend the detention of the aide, Eliezer Feldstein, and the military officer, who has not been publicly named. The men were arrested last month along with at least two other soldiers, who are being held under house arrest.

What’s the back story?

The Israeli authorities have been pursuing several lines of inquiry in recent weeks involving officials in Mr. Netanyahu’s office and several military officers. They are being investigated for trying to bolster Mr. Netanyahu’s reputation for his handling of the war, by leaking classified military documents, altering official transcripts of his conversations and intimidating people who controlled access to those records.

One strand of the investigation centers on the manipulation and publication of sensitive intelligence information that was leaked to the German newspaper Bild for an article that ran in September. The article cited a Hamas document laying out the group’s plan for psychological warfare against Israel on the hostage issue.

Critics viewed it as part of a disinformation campaign by Mr. Netanyahu or by his supporters, intended to dampen a popular push for the hostages’ release and to influence Israeli public opinion in favor of the prime minister’s negotiating positions.

Two weeks ago, the same judge, Menahem Mizrahi of the Rishon Lezion Magistrate’s Court, partly lifted a gag order to identify Mr. Feldstein, a civilian who was hired last year to work as a spokesman in Mr. Netanyahu’s office, as a main suspect in the case.

Mr. Netanyahu has not been questioned about the allegations, and his office has denied leaking information. Many details of the case have remained murky because of the gag order.

What’s new as more details have emerged?

In another partial lifting of the gag order on Sunday, the judge detailed how the document was leaked and why. He wrote that a noncommissioned officer in the military reserves, acting on his own initiative, illegally transferred the classified material to Mr. Feldstein via social media networks in April. Mr. Feldstein first tried to expose the information in the local news media, but Israel’s military censors barred its publication.

Mr. Feldstein and another colleague then bypassed the military censors by getting an article based on the document published abroad, and alerted the Israeli news media, expecting that they would quote it. Mr. Netanyahu also referred to the Bild article in remarks broadcast from a cabinet meeting.

After Israeli reporters questioned the authenticity of the document that formed the basis of the Bild report, Mr. Feldstein sought proof. He met with the noncommissioned officer, who gave him a physical copy of the document as well as two additional documents that were classified as top secret.

The officer and other suspects in the case have not been publicly named.

What did the judge say about motive?

In his decision on Sunday, Judge Mizrahi wrote that Mr. Feldstein’s actions were intended “to influence public opinion in Israel on the negotiations that were underway on the hostage issue and in particular, on the matter of the contribution of the protests to the strengthening of Hamas.”

The judge noted that Mr. Feldstein’s attempts to get the information published came soon after the Israeli military announced on Sept. 1 that six Israeli hostages had been found dead in a tunnel in Gaza after being shot by their captors, setting off widespread antigovernment protests. Mr. Feldstein’s actions, the judge wrote, stemmed from a “desire to change the public discourse and to turn the finger of blame” for the lack of an agreement toward Yahya Sinwar, the leader of Hamas, who was subsequently killed by Israeli forces in Gaza.

About 100 people taken captive by Hamas on Oct. 7, 2023, remain in Gaza. At least a third of them have been declared dead by the Israeli authorities.

Myra Noveck and Johnatan Reiss contributed reporting.

President Biden pledged new financial help to protect the Amazon, the planet’s largest tropical rainforest, during a visit to Brazil on Sunday, making one final push to combat climate change before President-elect Donald J. Trump returns to power in January.

After an aerial tour of one of the world’s most diverse ecosystems, Mr. Biden signed a proclamation declaring every Nov. 17 to be International Conservation Day and vowed that the United States would spend millions of dollars across the Amazon on restoring land, planting native tree species, supporting biodiversity efforts and increasing fertilizer efficiency programs. It was the first time a sitting American president had visited the Amazon.

“It’s often said that the Amazon is the lungs of the world,” Mr. Biden said during a brief stop in Manaus, a bustling city of two million nestled in the heart of the rainforest. “But in my view, our forest and national wonders are the heart and soul of the world,” he added. “The Amazon rainforest was built up over 15 million years. Fifteen million years history is literally watching us now.”

Flying low in his Marine One helicopter across the vast canopy of trees, Mr. Biden traveled along the Rio Negro, where its dark waters met the murky brown of the main Amazon River. From his helicopter, the president could see a wildlife refuge, shore erosion, fire damage and grounded ships, according to a map of the area provided by the White House.

But his initiatives may be short-lived. Environmental activists are bracing for a drastic shake-up in U.S. foreign policy under Mr. Trump, who has loudly opposed international cooperation on climate change. He has vowed to abandon global commitments and undo many of Mr. Biden’s environmental pledges.

Mr. Trump has said he will withdraw the United States — for a second time — from the landmark Paris climate accord, which aims to curb planet-warming emissions and rein in rising temperatures. He has promised to “drill, drill, drill” for oil and gas and nominated Chris Wright, a fossil fuels executive who has claimed “there is no climate crisis,” to lead the Department of Energy.

Top White House environmental officials said Sunday that some of the federal financing to protect the Amazon would go forward before Mr. Trump takes office, but not all of it.

In his remarks, Mr. Biden acknowledged the threat from Mr. Trump without using his name directly. But he expressed confidence that even his successor would not be able to stop efforts to protect the climate that also promote jobs and help make life better for people around the world.

“It’s true that some may seek to deny or delay the clean energy revolution that’s underway in America,” Mr. Biden said. “But nobody — nobody — can reverse. Nobody.”

“The question now,” he said, “is which government will stand in the way and which will seize the enormous economic opportunity.”

A U.S. rejection of the global climate agenda would come at a crucial time in the struggle to contain rising temperatures. Research shows that the earth has already warmed significantly, with the last decade being the hottest on record.

Mr. Biden has urged wealthy countries responsible for the bulk of the world’s emissions to help fund programs in poorer countries, where the effects of climate changes are often at their most severe.

In 2021, the United States was among more than 140 countries that vowed to end deforestation by 2030. Last year, Mr. Biden also pledged $500 million over five years to fight deforestation in Brazil, although the plan has met resistance from Congress and, so far, the South American nation has received only about 10 percent of the funding.

“The president has spoken frequently about the importance of U.S. leadership in protecting the Amazon and other tropical forests,” said Nigel Purvis, chief executive of Climate Advisers, a consulting firm.

The Amazon rainforest plays a crucial role in regulating the planet’s climate. Likened by scientists to a “giant air-conditioner,” the Amazon lowers temperatures, generates rainfall and stores vast quantities of planet-warming gasses.

After Mr. Biden landed in Manaus on Sunday, he came off the plane under scorching midday sun, looking relaxed and upbeat. He was accompanied by his daughter, granddaughter and aides and lingered on the tarmac before boarding one of seven helicopters waiting to take him on the aerial tour.

Mr. Biden took in the vastness of the rainforest, and the impact of climate change, at the Museum of the Amazon, an exhibition space and botanical garden in Manaus. He was greeted by three Indigenous women in traditional headdresses who chanted and shook rattles to the beat of an ancestral song. Overhead, macaws swept over the canopy, their noisy squawks echoing across the rainforest.

In recent decades, swaths of the Amazon have been razed and burned to make way for cattle ranches and soy farms. This both releases carbon and reduces the rainforest’s ability to capture it, dealing a double blow to efforts to rein in emissions.

As the destruction has advanced, parts of the rainforest have begun emitting more carbon that they store. And a glimpse into a future of recurrent droughts has rattled countries in the Amazon basin, parching stretches of the world’s largest river, triggering electricity shortages and stranding Indigenous villages.

A growing body of research warns that, if left unchecked, deforestation could push the Amazon to a tipping point that would transform it from a lush rainforest into a grassland savanna.

President Luiz Inácio Lula da Silva of Brazil has also been vocal about the need for wealthier countries to pitch in funds to help preserve the Amazon rainforest, about two-thirds of which lies within Brazil. He has been open about his anxieties about a U.S. pullback from the climate agenda, urging Mr. Trump during an interview with CNN this month to “think like an inhabitant of Planet Earth” when shaping his climate policies.

From Manaus, Mr. Biden is headed to Rio de Janeiro, where he will join a summit of leaders of the Group of 20 nations.

There, Mr. Biden’s allies will probably use the president’s last tour abroad to lock in partnerships on climate and other common goals — even if only as symbolic gestures that may be wiped out once Mr. Trump returns to power.

Catrin Einhorn contributed reporting.

Russia renewed its campaign to destroy Ukraine’s battered power grid on Sunday, targeting facilities across the country with missiles and long-range drones in one of the largest and most complex bombardments of the war, Ukrainian officials said.

The attack lasted several hours and featured around 120 missiles and 90 drones, President Volodymyr Zelensky said in a statement. Air-defense teams destroyed 144 targets, but at least nine civilians were killed, officials said. Mr. Zelensky said F-16 pilots had shot down 10 targets.

“The enemy’s target was our energy infrastructure throughout Ukraine,” Mr. Zelensky said. “Unfortunately, there is damage to objects from hits and falling debris.”

Later on Sunday night, a Russian rocket slammed into a residential apartment complex in Sumy, killing at least eight people, including two children, according to Ukrainian officials. The city is near the border with the Kursk region of Russia, where Russian forces have been trying to drive out Ukrainian soldiers who seized hundreds of square miles of territory this summer.

Earlier in the day, interceptor missiles could be seen streaking across blue skies over the Ukrainian capital, before exploding in thunderous claps. Similar scenes played out across Ukraine, Ukrainian officials said.

Russia used a combination of cruise and ballistic missiles fired from bombers, warships and land-based systems as well as swarms of drones from multiple directions. Ukraine had long expected a renewed attempt to collapse its energy grid, and it has come just as winter begins to bite.

Ukrainian officials said the attack was the latest demonstration that President Vladimir V. Putin of Russia remained bent not on a settlement but on the destruction of the Ukrainian state.

Ukraine’s foreign minister, Andrii Sybiha, said in a statement that the attack represented Mr. Putin’s “true response” to calls for peace. The minister added: “We need peace through strength, not appeasement.”

Precautionary emergency blackouts were announced across the country, and later Sunday, the national power utility, Ukrenergo, said restrictions on energy consumption would be needed nationwide on Monday. With explosions in nearly every region, the extent of the damage was not immediately clear.

Even when air defense does its job, the margin between life and death can be a matter of inches as debris rains down. Serhii Melnykov said he was walking near his home in Kyiv when he heard a powerful explosion, followed by an urgent call from his wife.

“She was trapped under the debris,” he said. “I immediately called the ambulance and rescuers, but by the time I got home, my wife, Anya, had already gotten out from under the rubble.”

She suffered a concussion and was in shock, he said, but was out of danger.

Rescue workers told him that they pulled a 600-pound fragment of a 3M22 Zircon hypersonic cruise missile from his apartment, he said.

Russian authorities have claimed that the Zircon can reach eight times the speed of sound, which would make it one of the fastest missiles in the world.

In both its size and variety, Ukrainian officials said the attack ranked as one of the most complex of the war. They also warned that Russia has been stockpiling missiles for months and would likely be able to carry out similar attacks in coming weeks.

Oleksandr Musiienko, head of the Center for Military Law Research, said that in addition to undermining the Ukrainian economy and causing pain, the attacks served a political goal for the Kremlin: demonstrating to President-elect Donald J. Trump “that there is no alternative but to force Ukraine to make concessions.”

He expected the attacks to continue as Mr. Putin tried “create a picture” that Ukraine was doomed.

The bombardment followed months of nightly attacks by long-range drones, an effort to wear down Ukrainian air defenses and terrorize civilians.

Before Sunday’s attacks, the United Nations warned that Russian strikes on Ukraine’s energy infrastructure could result in further mass displacement and deepen suffering for millions.

“If they were to target the energy sector again, this could be a tipping point,” Matthias Schmale, the U.N. humanitarian coordinator in Ukraine, said on Friday.

Years of relentless attacks have destroyed around 65 percent of Ukraine’s energy infrastructure, leaving Ukraine even more vulnerable this winter. Because Ukrainian cities have centralized systems for water, sewage and heating, power cuts put all those services at risk.

The renewed assault also comes as Ukrainian forces struggle to slow Russian advances in eastern Ukraine.

Mr. Zelensky acknowledged the difficult situation in a radio interview broadcast on Saturday with the Ukrainian public broadcaster Suspilne.

“There is slow, but nonetheless ongoing pressure and Russian advancement.” he said. “For various reasons: filling our brigades with trained personnel, equipping and supplying brigades with weapons — these processes have been quite slow.”

He said the war “will end faster with the policy” of a Trump administration but cautioned that Ukraine needed to strengthen its position on the battlefield to have a chance of negotiating a just and lasting peace.

Mr. Trump has vowed to bring the war to a quick end without saying how. On the campaign trail, he and some of his supporters cast doubt on his commitment to supporting Ukraine, leading to speculation that he might try to pressure Ukraine by withholding military aid.

Mr. Zelensky has said he has yet to hear anything of the sort from Mr. Trump, and has also repeatedly said that he sees no indication that Russia would be willing to negotiate in good faith.

“I don’t think Putin wants peace at all,” he told Suspilne.

With the Trump administration considering appointing a special envoy to mediate talks between Russia and Ukraine, Mr. Zelensky said it was important that America continue to recognize Russia as the aggressor.

“You can’t speak abstractly, ‘I’m a mediator, so I cannot choose one side or the other,’” he said. “This cannot happen when it’s about cases where international law was violated.”

Yurii Shyvala contributed reporting and Nataliia Novosolova contributed research.

Israeli airstrikes pummeled two areas in central Gaza and a town in the north of the enclave on Sunday morning, killing more than 30 people and wounding several others, according to local rescue and emergency services.

In central Gaza, a strike on a home in Nuseirat killed four people, the Palestinian Civil Defense said in a statement. Strikes in nearby Al Bureij killed 13 people, according to Mahmoud Basal, a spokesman for the Civil Defense, an emergency rescue group. He said that several others were wounded and that rescuers were still searching for people under the rubble.

The Israeli military did not immediately respond to a request for comment on the strikes in central Gaza, which came as it is waging a renewed offensive in the northern part of the enclave. In an effort to stamp out what the military has called a Hamas resurgence, Israeli troops, tanks and armed drones have bombarded northern Gaza almost daily.

On Sunday, the town of Beit Lahia again came under attack. Mr. Basal said that an Israeli strike on a house there killed 15 people, and that another strike hit a residential building where dozens of people were sheltering. Information on casualties from the strike on the residential building was not immediately available because rescue teams were unable to reach the area, he added.

When asked about Beit Lahia, the Israeli military said that it had carried out several strikes on “terrorist targets” in the town overnight and that there had been continuous efforts to evacuate the civilian population from northern Gaza, where its forces have been operating for over a month.

Gaza’s Civil Defense said it was forced to cease rescue operations in the north late last month because of attacks by the Israeli military on its members and destruction of its equipment.

The Israeli military said that two soldiers died in the fighting in northern Gaza on Sunday.

Gabby Sobelman contributed reporting from Rehovot, Israel.