Colombia refused to accept U.S. military planes deporting immigrants, setting off a furious reaction from President Trump, who on Sunday announced a barrage of tariffs and sanctions targeting the country, which has long been a top U.S. ally in Latin America.

The United States will immediately impose a 25 percent tariff on all Colombian imports, and will raise them to 50 percent in one week, Mr. Trump said on social media.

The Trump administration will also “fully impose” banking and financial sanctions against Colombia, and will apply a travel ban and revoke visas of Colombian government officials, the president said.

Colombia’s leftist president, Gustavo Petro, also hit back at Mr. Trump. In one social media post, he announced retaliatory tariffs of 25 percent on U.S. imports to Colombia and in another, longer post he said those tariffs would hit 50 percent.

Directly addressing Mr. Trump, Mr. Petro also questioned whether the American president was trying to topple him.

“You don’t like our freedom, fine,” Mr. Petro said. “I do not shake hands with white enslavers.”

The feud reflects how Mr. Trump is making an example out of Colombia as countries around the world grapple with how to prepare for the mass deportations of unauthorized immigrants that he has promised.

“This looks like a pretty bold and daring escalation on both sides,” said Will Freeman, a fellow for Latin America studies at the Council on Foreign Relations, citing Colombia’s economic reliance on the United States, which is still the South American country’s largest trading partner even as China has been making inroads.

“But equally, for Trump to threaten Colombia this way is pretty bold itself,” Mr. Freeman added. “That’s because Colombia remains historically the longest standing, the deepest, strategic ally in the region.”

Mr. Trump signed an executive order last week authorizing the U.S. military to assist in securing the border, and the Department of Defense said it would use military aircraft to deport people held in U.S. custody along the southern border.

Mr. Petro said earlier Sunday in a series of social media posts that Colombia would not accept military deportation flights from the United States until the Trump administration provided a process to treat Colombian migrants with “dignity and respect.”

Mr. Petro also said Colombia had already turned away military planes carrying Colombian deportees. While other countries in Latin America have raised concerns about Mr. Trump’s sweeping deportation plans, Colombia appears to be among the first to explicitly refuse to cooperate.

“I cannot make migrants stay in a country that does not want them,” Mr. Petro wrote, “but if that country sends them back, it should be with dignity and respect for them and for our country.” He said he was still open to receiving deportees on nonmilitary flights.

“Colombian President Petro had authorized flights and provided all needed authorizations and then canceled his authorization when the planes were in the air,” Secretary of State Marco Rubio said in a statement.

Mr. Petro’s office said in a statement that the presidential plane would be made available to transport the migrants who had been scheduled to arrive on the military planes. Representatives for Colombia’s Foreign Ministry did not immediately respond to requests for comment.

The immediate snag with the deportation flights appeared to be that U.S. military planes were transporting the undocumented migrants, a U.S. military official said on Sunday.

The two U.S. aircraft that were denied the ability to land in Colombia were Air Force C-17 transport planes. One turned around and returned to San Diego; the other flew back to Texas.

If the migrants were shifted to a commercial or charter flight, at least until diplomatic clearances had been settled for the government planes, the issue might resolve itself, said the military official, who spoke on condition of anonymity to discuss operational matters.

President Petro’s remarks came in response to a post about the treatment of Brazilian deportees. Brazil’s foreign ministry complained of “degrading treatment” of its citizens after 88 migrants arrived in the country handcuffed on Friday and some complained of mistreatment after not being given water or allowed to use the bathroom during the flight.

Since taking office last Monday, Mr. Trump has issued a series of executive orders and made other moves aimed at laying the groundwork to deport an enormous number of migrants.

In his missive on social media, Mr. Trump called Mr. Petro, a former left-wing guerrilla, a “socialist,” a term that Mr. Petro has no problem in using to describe himself, and contended that Mr. Petro was “very unpopular.” Mr. Petro’s approval ratings stand at around 34 percent, as he has been weighed down by corruption scandals and a resurgence in fighting among armed groups.

To justify his measures targeting Colombia, Mr. Trump also claimed that the military deportation flights refused landing by Mr. Petro included a “large number of Illegal Criminals” and that the United States was seeking the “return of the Criminals they forced into the United States.”

The U.S. tariffs could deal a significant blow to Colombia’s economy. The United States is Colombia’s largest trading partner, with top Colombian exports to the American market including crude oil, coffee and cut flowers.

Trade between the two countries totaled $53.5 billion in 2022, with the United States having a trade surplus of $3.9 billion that year. Colombia is the largest South American market for U.S. agricultural products, absorbing imports of American pork, dairy products, alcoholic beverages and dog and cat food.

Mr. Petro also cast attention on Americans living in Colombia, saying more than 15,000 Americans were living in the country without authorization, and calling upon them to “regularize” their immigration status.

Colombia is not among countries with the largest unauthorized immigrant populations in the United States, trailing far behind Mexico, El Salvador, India, Guatemala and Honduras. In 2022, Mexicans remained the most common nationality among unauthorized immigrants in the United States, with about 4 million, while Colombia had about 190,000, according to the most recent data available from the Pew Research Center.

Colombia has traditionally been a close U.S. ally, though differences have recently emerged regarding counternarcotics policies. While Mr. Petro has criticized the United States more than past presidents, he continued to collaborate with the United States and regularly accepted deportation flights, said Sergio Guzmán, a Colombian political analyst.

This is what “makes this new approach so surprising,” he added.

Mr. Petro, who took office in 2022, is Colombian’s first leftist president, and a longtime leader in Colombian politics known for his bullish, combative stances, particularly when it comes to defending human rights.

A former rebel who later demobilized and became a senator, his critics say he sometimes acts rashly and refuses to listen to advisers.

He has long been critical of the outsize power the United States holds in the world, particularly of the economic imbalance between the U.S. and other nations.

The acting secretary of defense, Robert G. Salesses, said in a statement last week that the military would provide airplanes to support with deportation flights sent by the U.S. Department of Homeland Security, which oversees ICE.

The Trump administration is sending the military planes in addition to the usual flights operated by ICE, meaning that they do not replace the typical flights that land several times a week in countries throughout the region, and which Mr. Petro referred to in his online posts on Sunday as “civilian flights.”

The new planes sent by the military can only depart from the United States if the receiving nation has approved them.

It is unclear which countries may have agreed to receive military planes carrying deportees.

Early on Friday, Guatemala received two U.S. Air Force jets carrying around 160 deportees in total, making it one of the first countries to publicly receive such flights.

Officials in Mexico, the source of the largest number of unauthorized immigrants in the United States, have said they remained open to receiving deported citizens and routine deportations have taken place to Mexican cities along the U.S. border in recent days.

Still, Mexican authorities have not disclosed whether they plan to accept military flights or whether they will receive deported migrants from other countries, as Mexico has sometimes done in the past.

On Friday, NBC reported that Mexico had refused to authorize a military plane carrying deportees from the U.S., an account that could not be independently confirmed.

Honduras, which like Colombia has pushed back against the Trump administration’s plans for mass deportations, has said it is open to receiving military flights.

Eric Schmitt contributed reporting from Washington, Jack Nicas from Rio de Janeiro, Julie Turkewitz from Bogotá, and Jody García from Guatemala City, Guatemala.

It was a contentious, aggressive telephone call, five days before the inauguration of President Trump on Jan. 20.

Speaking to Prime Minister Mette Frederiksen of Denmark, Mr. Trump insisted he wanted the United States to take over Greenland, the massive and autonomous Danish island that occupies a strategic part of the ocean as the ice caps melt and new shipping lanes open up.

The tone and content of the icy exchange was described by two European officials who were briefed on the 45-minute call and requested anonymity because of the sensitivity of the topic. The United States has not publicly commented on the call.

Ms. Frederiksen made various suggestions for more cooperation on military and economic issues, but insisted that Greenland, which already hosts an important American base, was not for sale, according to the European officials.

Since that Jan. 15 call, whose aggressive tenor was earlier reported by The Financial Times, Denmark has tried to calm the waters, urging its partners in the European Union not to inflame the situation until matters become more clear, the officials said. The issue of Greenland is not on the agenda for an E.U. foreign affairs council meeting in Brussels on Monday, for example.

If Mr. Trump decides to pressure Denmark with economic means, through tariffs, the European Union itself would be expected to respond as a whole with countertariffs, said Zaki Laïdi, a professor at Sciences Po and an adviser to the former E.U. foreign policy chief, Josep Borrell Fontelles.

“I was told that Trump is quite serious about Greenland, and it’s going to be a huge challenge for the E.U., if we don’t react strongly to it,” Mr. Laïdi said. He confirmed that “the Danes are saying, ‘Keep it down,’ but they’re scared.”

That sense of foreboding was obvious in Davos, Switzerland, where European leaders gathered last week with corporate executives and academics for the World Economic Forum’s annual meeting. Rumors about Mr. Trump’s call with Ms. Frederiksen were rampant at the gathering, as was nervousness about what a second Trump administration will mean for Europe as a whole.

For now, the Danes are concentrating on dialogue. On Friday, Lars Lokke Rasmussen, Denmark’s foreign minister and prime minister during the first Trump administration, had a 20-minute telephone discussion with the new U.S. secretary of state, Marco Rubio. Afterward, Mr. Rasmussen said that the two countries had agreed to discuss “the Arctic region” and that the conversation, which included other issues like Ukraine, had a “good and constructive tone.”

The State Department, for its part, said that Mr. Rubio had “reaffirmed the strength of the relationship” between the two countries. The two men, the State Department said, “discussed the importance of deepening bilateral and regional cooperation on security and defense, economic and trade matters, and ending the war in Ukraine.”

Officially, Denmark has said little about the phone call between Mr. Trump and Ms. Frederiksen. A statement from Ms. Frederiksen’s office immediately afterward made no mention of sharp disagreements but emphasized trade with the United States and talked of cooperation, dialogue and enhanced investment in security by Denmark.

“In the conversation, the Prime Minister emphasized the importance of strengthening security in the Arctic, and that the Kingdom of Denmark is ready to shoulder even greater responsibility for this,” the statement said. In the statement, Ms. Frederiksen cited the chairman of the Greenlandic Parliament, Mute Egede, saying that Greenland is not for sale and argued that “it is up to Greenland itself to make a decision on independence.”

The officials who were briefed on the phone call and Mr. Laïdi suggested that Mr. Trump’s intentions were unclear, and that he might move to encourage Greenlanders to vote for independence in a referendum and then to bind themselves to the United States. Or he may want to pressure Denmark and the European Union with tariffs. Brussels is working with the Danes to strike the right tone and to figure out what Mr. Trump really wants, one official said.

In a response to questions on Sunday, the Danish prime minister’s office said it did “not recognize the interpretation of the conversation given by anonymous sources.”

Under a 2009 agreement with Denmark, Greenland can declare independence only after a successful referendum — which Mr. Egede has suggested might be held in tandem with the island’s upcoming parliamentary election in April.

Mr. Trump has called U.S. control over Greenland “an absolute necessity” for Western security, and on Saturday, in a gaggle with reporters, said “I think we’re going to have it.”

Friis Arne Petersen, a former Danish ambassador to Washington, said that “Europe, Greenland and the rest of the world must take Donald Trump’s statements very seriously, because they were carefully prepared.”

“The terms used and their context left no room for interpretation,” he said in an interview with the French newspaper Le Figaro. Mr. Trump’s interest in Greenland was more commercial in his first term — when he first offered to buy it — but is now predominantly about security, Mr. Petersen said.

The issue of Greenland “is of the utmost importance to the E.U.,” Mr. Laïdi said. “Our credibility is at stake. The Danish want to keep a low profile but that’s not the way the world works.”

Greenland, with a population of around 60,000, was a Danish colony until 1953, and became self-ruling with its own Parliament in 1979. It remains a territory of Denmark, with Copenhagen exercising control over its foreign and defense policy.

Europe’s longest-serving leader, President Aleksandr G. Lukashenko of Belarus, cruised to his seventh election victory in a row on Sunday in a contest that his exiled opponents dismissed as a sham whose only purpose was to cement his autocratic grip on the former Soviet republic, Russia’s closest ally.

“Don’t use the word election to describe this farce,” said Svetlana Tikhanovskaya, an opposition leader who fled Belarus after the country’s previous presidential vote in 2020 and a brutal crackdown on nationwide protests over election fraud. “It is a staged performance by Lukashenko to cling to power at any cost.”

A survey of voters leaving polling places that was released by state media on Sunday evening showed Mr. Lukashenko getting 87.6 percent of the vote, more than the 81 percent he claimed to have won in 2020. Exit polls are controlled by the state like all aspects of elections in Belarus and generally reflect the ultimate outcome.

Unlike in 2020, when Ms. Tikhanovskaya was allowed to run against Mr. Lukashenko and declared herself the winner, Sunday’s election was a tightly controlled and tame affair, featuring only candidates loyal to the president. None expressed any desire to actually defeat Mr. Lukashenko, who has ruled Belarus with an iron fist since 1994.

Ms. Tikhanovskaya, out of the country since 2020, did not take part in Sunday’s election and was instead in Warsaw, leading a protest against Mr. Lukashenko, who mocked her efforts and claimed that President Trump had cut off funding to her opposition movement in exile. He appeared to be referring to an executive order last week that halted virtually all foreign aid for a 90-day reassessment period.

Three candidates running against Mr. Lukashenko, according to the exit poll, garnered less than two percent of the vote each. A fourth, the leader of the Communist Party, Sergei Syrankov, captured 2.7 percent.

At a televised election debate last week, which the president did not join, Mr. Syrankov, saying said he wanted to be “honest,” acknowledged: “Everyone in this studio knows that Aleksandr Lukashenko is going to win.”

With all of Mr. Lukashenko’s prominent opponents either in jail or in exile and Belarus’s media outlets all cheering for the incumbent, the result was a foregone conclusion. But it is one that still mattered to the president, who is eager to show his country — and also President Vladimir V. Putin of Russia — that the turmoil of 2020 has been tamed.

In a statement on Sunday, the European Union’s foreign policy chief, Kaja Kallas, described the election as a “sham” that “has been neither free, nor fair.”

But foreign election observers, drawn from far-right political parties like Alternative for Germany and other pro-Russian groups, hailed the vote as a triumph for democracy and denounced tart criticism of the election by the European Parliament and other institutions. “They say that there is a dictatorship here, but I don’t think so — the reality in Belarus is completely different,” Krastyo Vrachev, an observer representing a fringe nationalist party from Bulgaria, told Belarus’s state news agency. “People are calm and communicate with ease; in Europe this is not at all the case,” he added.

The election was certainly calm, so much so that Mr. Lukashenko barely bothered to campaign, saying he was too busy to take part in a debate with four state-selected rival candidates or to hold rallies. In a nod to conventional politics, however, last week he signed a decree raising pensions by 10 percent starting Feb. 1.

A recent survey of public opinion in Belarus by Chatham House, a British research group, indicated widespread dissatisfaction with the economy, which has been hit hard by economic sanctions imposed on the country over its support for Russia’s February 2022 invasion of Ukraine. Just 11 percent of respondents were definitely satisfied with the economy, while only 32 percent said they supported Russia’s invasion.

Mr. Lukashenko’s main appeal, according to the survey, is his “favorable image” as a “politician striving to prevent Belarus from being involved in the military conflict following the Russian invasion of Ukraine.”

Russian troops used Belarus as a staging ground for an initial, abortive thrust toward Kyiv in early 2022, but Mr. Lukashenko has resisted pressure from Moscow to send Belarus’s troops to join the fight against Ukraine.

After casting his vote Sunday in Minsk, the capital of Belarus, Mr. Lukashenko predicted that “there will be some kind of resolution this year,” to the conflict, adding that President Trump “is not an idiot, not a fool” and recognizes that “you can’t push us around,” referring to Belarus and Russia. “We will see light at the end of the tunnel this year,” he said of the war.

His nominal rivals in Sunday’s vote all avoided criticism of Mr. Lukashenko, who brooks no open dissent and has embraced his moniker as “Europe’s last dictator,” an insult coined in 2005 by the U. S. secretary of state at the time, Condoleezza Rice.

While delighting in taunting the West, particularly neighboring Poland, and displaying his loyalty to Moscow, Mr. Lukashenko has in recent months signaled a desire to improve frosty relations with Western capitals by releasing political prisoners.

This process, widely seen as an effort to get relief from Western sanctions, continued on Friday when Mr. Lukashenko pardoned 15 more prisoners, including five people jailed for “extremist crimes,” a blanket term used to describe criticism of the president. The names of those released were not made public.

Secretary of State Marco Rubio, in a social media post on Sunday, indicated that they included a United States citizen whom he identified as Anastasia Nuhfer, “who was taken under JOE BIDEN!” he said in the post. Mr. Rubio said Ms. Nuhfer had been “unilaterally released,” thanks to President Trump’s leadership.

At a news conference in Minsk on Sunday, Mr. Lukashenko denied that he was releasing prisoners to curry favor abroad, saying, “I don’t give a damn about the West.” He said his decision to set some people free “is based on the principle of humanity.”

None of Mr. Lukashenko’s most prominent opponents, who include Ms. Tikhanovskaya’s husband, Sergei, have been set free. The United States and the European Union have left sanctions in place.

In a sign that the authorities are hoping for a more sympathetic hearing from the new Trump administration, Belarus’s state media last week reported gleefully that, following the inauguration in Washington, the State Department had removed from its website a statement critical of Sunday’s election that had been made by the outgoing secretary of state, Antony J. Blinken.

Mr. Blinken’s deleted statement denounced the Belarus election as a farce, saying, “The United States joins many of our European allies in assessing that elections cannot be credible in an environment where censorship is ubiquitous and independent media outlets no longer exist.”

A suggestion by President Trump to “clean out” the Gaza Strip and ask Egypt and Jordan to take in more Palestinians raised new questions on Sunday about United States policy toward the Israeli-Palestinian conflict and drew flat rejections from two of its most important allies in the Middle East.

Mr. Trump’s comments appeared to echo the wishes of the Israeli far right that Palestinians be encouraged to leave Gaza — an idea that goes to the heart of Palestinian fears that they will be driven from their remaining homelands, but one that was dismissed by Egypt and Jordan.

“You’re talking about probably a million and a half people, and we just clean out that whole thing,” Mr. Trump said of Gaza on Saturday. “I don’t know. Something has to happen, but it’s literally a demolition site right now.”

Mr. Trump told reporters on Air Force One that he had spoken to King Abdullah II of Jordan, saying, “I said to him, ‘I’d love for you to take on more because I’m looking at the whole Gaza Strip right now, and it’s a mess.’” He said that he would also like Egypt to take in more Palestinians and that he would speak to the country’s president, Abdel Fattah el-Sisi.

He said Palestinians could be in Jordan and Egypt “temporarily, or could be long-term.”

It was unclear from Mr. Trump’s comments if he was suggesting that all of the people in Gaza leave. The enclave has a population of about two million.

The suggestion by Mr. Trump was rejected Sunday by both Egypt and Jordan, which both emphasized that the only way forward was Palestinian statehood.

Egypt’s Foreign Ministry released a statement saying that any attempt to uproot Palestinians from their land, whether through settlement, annexation, displacement or transfer, would be a “violation” that “threatens stability and risks escalating the conflict in the region.”

The Jordanian foreign minister, Ayman Safadi, said in a meeting with a United Nations official that Jordan’s rejection of displacement was “unchangeable,” and seen as essential to regional stability, according to Petra, the official Jordanian news agency. He added, “Jordan is for Jordanians, and Palestine is for Palestinians.”

Hamas, the militant group that runs Gaza, and Fatah, the Palestinian political movement that dominates the Palestinian Authority, also condemned the idea.

“The Palestinian people in the Gaza Strip have endured death and destruction over 15 months in one of humanity’s greatest crimes of the 21st century, simply to stay on their land and homeland,” said Basem Naim, a member of the Hamas political bureau, referring to the war that started with the Hamas-led attack on Israel in 2023. “Therefore, they will not accept any proposals or solutions, even if seemingly well-intentioned under the guise of reconstruction, as proposed by U.S. President Trump.”

But the idea appeared to be welcomed by hard-line Israeli politicians.

Bezalel Smotrich, the far-right finance minister in the government of Prime Minister Benjamin Netanyahu, posted a statement on X on Sunday that seemed to refer to Mr. Trump’s comments, although he did not mention the U.S. president.

“After 76 years in which most of the population of Gaza was held by force under harsh conditions to maintain the ambition to destroy the State of Israel, the idea of ​​helping them find other places to start a new, good life is a great idea,” he said.

Mr. Smotrich has long advocated for helping Gazans who want to leave to depart, and for the Israeli military to remain in the enclave to help pave the way for eventual Jewish settlement there.

Millions of Palestinian refugees are already living in camps in Jordan, Syria and Lebanon, while others now live in other Arab countries — including Egypt and the United Arab Emirates — and around the world. But Palestinians and their Arab allies have long rejected any further resettlement outside Palestinian territories, saying that forcing Palestinians to leave would mean erasing any hope of a future Palestinian state. Without land, they say, there is no country.

Virtually all Egyptians and Jordanians fervently support Palestinian aspirations for statehood, making it unlikely that either government would consent to such arrangement.

“This would be going against its base completely,” Maged Mandour, an Egyptian political analyst, said of the prospects of Egypt taking in large numbers of Palestinians. “It’s just a non-starter.”

Egypt also fears that the arrival of large numbers of Palestinians could threaten the country’s security. In particular, Cairo has long been concerned that embittered, impoverished Palestinian refugees, if allowed into Egypt, could launch attacks on Israel from Egyptian soil, drawing Israeli retaliation.

Early in the war, Egypt became so concerned about the prospect of any move that would send Gazans spilling into its territory that it warned Israel that it was jeopardizing the decades-old Israel-Egypt peace treaty, an anchor of Middle East stability since 1979.

Jordan is already home to many Palestinians and many Jordanians of Palestinian descent. Accepting refugees from Gaza would risk destabilizing a population that has never resolved tensions stemming from the original influx of Palestinians, analysts say.

It is unclear whether Mr. Trump’s comment signals a change in U.S. policy toward Palestinians.

Under President Joseph R. Biden Jr. and other recent presidents other than Mr. Trump, the United States officially supported establishing a Palestinian state alongside an Israeli one, criticized Israeli extremist attempts at seizing more Palestinian land by building settlements on it and assured Egypt and Jordan that they would not be forced to take in more Palestinians.

But with Mr. Trump’s return to the White House, all of the assumptions that had undergirded American relationships in the Middle East may now be upended.

Egypt and Jordan are both major U.S. partners in the region, and successive U.S. administrations have regarded their stability as crucial to that of the wider Middle East. They both receive significant U.S. funding, with Egypt the second-largest recipient of foreign aid after Israel.

The Trump administration issued a memo on Friday suddenly freezing all foreign aid for a 90-day reassessment period, but laid out two major exceptions: weapons support to Israel and Egypt. The same day, in a further sign of Mr. Trump’s support for Israel, the White House told the Pentagon to proceed with a shipment of 2,000-pound bombs to Israel that Mr. Biden abruptly stopped last summer to discourage the Israeli military from destroying much of the Gazan city of Rafah. Israeli forces bombed the city anyway.

It is unclear if Mr. Trump would try to use the $1.3 billion that Egypt is supposed to receive in annual aid as leverage to try to force it to accept more Palestinian refugees.

The fear of being driven from Gaza runs deep among Palestinians, who reject it as a replay of what they call the Nakba — or “catastrophe” in Arabic — the mass displacement of Palestinians from their homes in 1948 during the war surrounding Israel’s creation as a state.

Hundreds of thousands of Palestinians in Gaza are trying to return to their homes as the cease-fire between Hamas and Israel enters a second week. It is only the second pause in fighting between the two since Oct. 7, 2023, when Hamas led an attack on Israel that killed more than 1,200 Israelis. Since then, Israel’s military has killed at least 46,000 Palestinians, according to Gazan health officials, who do not distinguish between combatants and civilians. It has also destroyed thousands of homes and buildings in Gaza and killed many of Hamas’s leaders.

Most of the two million Palestinians in Gaza have had to flee their homes at least once. And though aid in recent days has increased, the humanitarian situation remains dire, with water, food and medicine running low and few working hospitals left.

Noura al-Awad, 29, and her family were some of those who stayed put in their homes in Gaza City for the last 15 months, persisting through airstrikes, a ground invasion and near-famine conditions because they were determined not to cede their land to Israel, she said in a phone interview on Sunday.

She vowed to outlast Mr. Trump’s plans, too.

“For one year and three months, we were attacked from all sides, we got starved and humiliated, we experienced killing, death and destruction, but we didn’t move south,” she said. “No way” would she leave, she said.

Reporting was contributed by Andrés R. Martínez, Iyad Abuheweila, Isabel Kershner and Rania Khaled.

When a 28-year-old volunteer named Nikolai stepped onto a sandy beach on Russia’s Black Sea coast in a hazmat suit just before New Year’s Eve, he was so overwhelmed by the amount of thick oil film that he almost broke down.

He and other volunteers were tasked with shoveling away the oil-drenched sand, but “the scale is just too big,” he said.

Two weeks into the new year, and four weeks after the spill, President Vladimir V. Putin acknowledged the extent of the disaster and dispatched senior officials to deal with Russia’s largest oil spill in years, which has befouled some of the country’s most popular beaches.

The oil was released by two aging Russian tankers that were damaged during a heavy storm in the Kerch Strait on Dec. 15. At least 2,400 metric tons of oil spewed into the sea, Russian officials said.

The disaster in the strait, which separates the Crimean Peninsula from Russia, raised questions about whether the vessels were part of the so-called shadow fleet that Moscow uses to evade sanctions on its oil industry, sometimes employing ships in shoddy conditions.

One of the vessels, the Volgoneft-212, split in half and sank, killing one crew member. The other, the Volgoneft-239, ran aground near the port of Taman. The two vessels were loaded with a total of 9,000 tons of heavy fuel oil, and the authorities are now working not only to clean up the shores, but also to try to contain additional spills from the ship that ran aground.

Russian officials originally claimed that the spill was contained, but soon after the disaster, sightings of floating oil and tarred birds were reported all along Russia’s Black Sea coast.

On Sunday, the government said it was allocating another 1.5 billion rubles (about $15.3 million) to the cleanup effort, drawing the money from its reserve fund. Three days earlier Mr. Putin ordered a report on the condition of Russia’s tanker fleet, and also asked a deputy prime minister to review Russian legislation covering oil shipments by sea and river and to look into the “scientific advances on the cleanup of similar disasters,” his press office said.

Last week, the Ukrainian Navy warned that oil from the spill could reach Ukraine’s Black Sea coast near Odesa and Mykolaiv, but Ukraine’s Environmental Ministry said a day later that it saw no immediate threat.

Nikolai was among hundreds of volunteers who have lent a hand to the cleanup. A Moscow entrepreneur, he had viewed information from photographs and videos posted by local residents and officials, and traveled to the resort town of Anapa as the new year approached.

In a phone interview with The New York Times after he returned home, he said he had spent a week shoveling away the oil that was washing onto the shore. He asked that his surname not be used because he fears he might lose out on state contracts.

Individuals and businesses chipped in to provide some volunteers with hazmat suits and some basic equipment, but the task was daunting.

“I had seen the photos before I arrived,” Nikolai said. “Yes, it looked bad — but it’s different when you see it in real life. You take the shovel and scoop out that black blob of oil, and it feels like just a drop in the ocean.”

The air along the coast was so heavy with oil fumes, Nikolai said, that he felt dizzy and weak after walking there without a respirator.

Cleanup teams have been responding to oil spills along a coastline of almost 500 miles, collecting over 160,000 tons of contaminated sand and soil as well as 25 tons of “oil-containing liquid,” Russia’s Emergency Situations Ministry said this week.

But the spill risks becoming a “long-term environmental disaster,” according to Greenpeace Ukraine, which criticized the slow Russian response and warned of a deadly impact on Black Sea marine life.

Environmentalists say the spill is particularly difficult to clean up because of the tankers’ cargo. Heavy fuel oil, unlike ordinary regular crude oil, does not stay on the surface of the water, but instead sinks to the bottom.

“If it is not promptly removed from the surface, it remains to wait until it is biodegraded by marine microorganisms,” said Natalia Gozak, the office director of Greenpeace Ukraine. “This can take decades.”

The lack of an immediate response means that large masses of contaminated sand need to be scooped out, essentially gutting the portions of the beaches around Anapa, according to Georgy Kavanosyan, an independent Russian environmentalist and hydrogeologist who arrived at the scene two days after the spill.

“The oil started sinking down into the sand in the initial days because there were not enough responders there,” Mr. Kavanosyan said.

Satellite images published by Mr. Kavanosyan showed two elongated stains near the tanker that ran aground, indicating new oil spills from it after two minor earthquakes in the area over the weekend.

“That vessel is a ticking bomb,” he said. “The most important thing right now is to pump out that oil and extract the ship.”

Officials reported that they had collected most of the oil from that spill by last Monday.

When Mr. Putin finally spoke out about the disaster, he described it as “one of the most serious environmental challenges we have faced in recent years.”

Mr. Putin ordered senior officials dispatched to oversee the efforts. A task force set up this month brought in several ministers to make plans for the cleanup and reconstruction, as well as for removing the tankers.

The oil spill’s longer-term effect on wildlife remains to be seen.

At least 58 dead dolphins have been found so far, the Delfa Dolphin Rescue and Research Center said in a statement on Saturday. The group sent a team out to the sea last Friday to reach the sunken tanker and confirm reports that the oil was still seeping out from it.

“Contamination was along the entire route,” it said. “Just five kilometers from the shore, common bottlenose dolphins and harbor porpoises were swimming in oil film and small fractions of fuel oil, to our great regret and alarm.”

At least 6,000 oil-smeared birds have been caught and cleaned by volunteers, but many are unlikely to survive, experts said. The spills are likely to kill tens of thousands of local birds, according to Greenpeace Ukraine.

Russian oil companies have increasingly turned to using dilapidated tankers that are not regulated or insured by Western companies.

President Volodymyr Zelensky of Ukraine and other Ukrainian officials have suggested the two 50-year-old tankers were part of Russia’s shadow fleet, which emerged after Western nation moved to punish Moscow economically over the invasion of Ukraine.

But Elisabeth Braw, a senior fellow at the Atlantic Council who has written several articles on the shadow fleet, said the ships were “rickety old tankers” that lacked several characteristics of shadow fleet vessels, which typically operate in the Baltic Sea and sail under the flags of other countries.

Both tankers involved in the spills are Russian-owned, and one of them had its license suspended and should not have been allowed to sail, according to the state-owned RIA Novosti news agency.

Questions were also raised about why the tankers, originally built for river navigation, were allowed at sea in winter storms in the first place.

Cassandra Vinograd contributed reporting from Kyiv, Ukraine.