“The Israeli settlements in the West Bank and East Jerusalem and the regime associated with them have been established and are being maintained in violation of international law,” the court’s president, Nawaf Salam, said as he issued the 83-page opinion at the Peace Palace in The Hague.

The court also said that Israel’s presence in the territories should come to an end “as rapidly as possible” and that Israel was “under an obligation to provide full reparation for the damage caused by its internationally wrongful acts to all natural or legal persons concerned.”

Friday’s pronouncement received heightened attention because of the war in Gaza, which began more than nine months ago, and because of a separate genocide case brought in the same court by South Africa against Israel in December over its conduct in the war.

In an initial ruling on the genocide case in January, the court ordered Israel to restrain its attacks in Gaza, and in May it ordered the country to immediately halt its military offensive in the city of Rafah, in southern Gaza.

The U.N. General Assembly in 2022 asked the court for its opinion on the legal consequences of Israel’s “prolonged occupation, settlement and annexation” of territories captured in the 1967 Middle East war, including the West Bank, Gaza and East Jerusalem.

Prime Minister Benjamin Netanyahu of Israel called the decision “mendacious” and said that Israeli settlement in all parts of its land was legal.

“The Jewish people is not an occupier in its land — not in our eternal capital Jerusalem and not in the tracks of our forefathers in Judea and Samaria,” he said, using the Israeli designation for the territories that make up the West Bank.

In his response, Israel’s far-right finance minister, Bezalel Smotrich, posted an Israeli flag emoji on social media and added: “The answer to The Hague — sovereignty now.” The comment reflected the view of many Israeli religious nationalists and settlers that the government should declare the occupied lands part of Israel.

Many Palestinians were likely to welcome the court’s opinion as a vindication and the Palestinian Authority said in a statement that it was a “victory for justice” as it “affirmed that the Israeli occupation is illegal.”

Israel annexed East Jerusalem decades ago, in a move that did not garner widespread international recognition.

The country regards the occupied West Bank as disputed territory and wants the future status of it to be decided in negotiations, but it has allowed hundreds of thousands of Jews to settle there, on land envisioned by Palestinians — and many of Israel’s allies — as part of a future Palestinian state. Critics say the settlements carve the West Bank into a patchwork that make a potential state increasingly untenable, while many settlement advocates oppose Palestinian statehood and support annexation by Israel.

Israel withdrew from Gaza and dismantled its settlements there in 2005 but partly blockaded the territory, along with Egypt, for 17 years after Hamas seized control of it in 2007. Now much of Gaza is once again under Israeli military control.

Mr. Netanyahu’s government receives diplomatic, economic and military support from the United States and other allies and so appears in a strong position to disregard the opinion. But analysts said it was nevertheless significant, not least because of the strength of the court’s language and the scope of its opinion.

Nomi Bar-Yaacov, an international lawyer and an expert on Middle East politics at Chatham House, a research group in London, called the opinion a “legal earthquake” and said it was the strongest opinion that the court had ever issued.

“It’s a sign that the occupation has gone on for too long and not enough efforts by the parties and by the international communities has been made to resolve the issue,” she said, adding that the opinion might paradoxically strengthen the far right coalition’s push for annexation.

Michael Milshtein, an analyst of Palestinian affairs at Tel Aviv University, said a dramatic Israeli government reaction to the court’s opinion would be unlikely in the short term because of Mr. Netanyahu’s planned visit to Washington next week, and it would “create another headache.”

Other analysts said that the opinion would be impossible for some foreign governments to disregard.

“It could influence the foreign policies of certain European countries,” said Yuval Shany, a senior fellow at the Israel Democracy Institute, noting that Norway, Spain, Ireland and Slovenia have in recent weeks joined more than 140 other countries in recognizing a Palestinian state.

The international court held hearings in February at the Peace Palace. Israel did not appear at that session but filed a submission rejecting the validity of the proceedings as biased. The Palestinian Authority’s foreign minister, Riyad al-Maliki, told the court that Israel had subjected Palestinians to decades of discrimination, leaving them with the choice of “displacement, subjugation or death.”

Over the course of several days, representatives of more than 50 countries, an unusually high number for the court, addressed the hearings. Most sided with the Palestinian representatives. But a few speakers at the court, including those from the United States, Britain and Hungary — among Israel’s traditional allies — sided with Israel.

A U.S. State Department official argued before the court that Israel’s policies toward the Palestinians were determined by its “very real security needs.”

Two focal points of Friday’s case were Israel’s settlement policy in the West Bank and East Jerusalem as well as the government’s tolerance of violent land grabs by Jewish settlers.

Every Israeli government has allowed some Israeli construction in the territories, but the Netanyahu government has expanded the program and announced plans for thousands of new housing units. More than 500,000 Israelis have settled in the West Bank since 1967 and there are 2.7 million Palestinians in the territory.

“We are investigating why we did not identify it, attack it and intercept it,” Admiral Hagari said.

An Israeli military official, who briefed reporters on condition of anonymity, said there was a possibility that human error might have allowed the drone to penetrate Israeli airspace, rather than a gap in the military’s detection systems.

The Israeli military said the drone had likely flown from Yemen, where the Houthis are based, before approaching Tel Aviv from the coast. Video posted on X and verified by The New York Times shows what appears to be a unmanned aerial vehicle approaching west of Tel Aviv, followed by a blast at the location of the strike.

Pentagon officials expressed doubts that the Houthis were specifically targeting the U.S. diplomatic building, but could not rule it out.

It appeared to be the first time the Houthis had struck at such long range, more than 1,100 miles from the nearest Yemeni territory. “All Israeli cities have now come under the reach of our targeting,” a Houthi brigadier general, Abed Al-Thawr, said in an interview. He added, “There are weapons that haven’t been unveiled yet.”

The two sides offered differing accounts of the type of drone used in the attack.

Nasruddin Amer, a Houthi spokesman, said in an interview that the drone, called Yaffa, had been fully manufactured in Yemen and that it had not previously been used for direct operational purposes. He said the drone bore technologies that made it difficult to detect.

But Admiral Hagari told reporters that the drone was a Samad-3, an Iranian model, that had been adapted for long-distance flight. He denied that it had stealth capabilities that enabled it to evade Israeli surveillance.

Mr. Amer said that the attack was a response to “an escalation in massacres against the Palestinian people in Gaza,” and that the Houthis would halt their assaults only when the war in Gaza ends and Israel’s blockade of the enclave is lifted. He added that Iran was not involved in the decision to carry out the attack on Tel Aviv, but he said the Houthis had updated the Iranians afterward.

Israel’s defense minister, Yoav Gallant, said in a statement that “anyone who tries to harm the state of Israel or sends terror against it” will meet an Israeli response “in a sharp and surprising way.”

Asked whether Israel would respond to Friday’s attack, Admiral Hagari said it would first work to fully assess the situation.

Iran-backed militants across the Middle East have fired masses of rockets and drones at Israel since Hamas’s Oct. 7 attack triggered Israel’s devastating campaign in Gaza. Israel has intercepted most of them, leaving central Israel mostly unscathed in recent months — until Friday, when the explosive-laden drone struck the building just after 3 a.m.

Since November, the Houthis have also been attacking ships along a vital route in the Red Sea in what they have described as a campaign in solidarity with Palestinians in Gaza. Admiral Hagari said that dozens of drones had been launched at Israel from Yemen since the war with Hamas began in October, most of which were intercepted by American or Israeli forces.

Hezbollah, based in Lebanon, has launched thousands of strikes on northern Israel since the start of the war, many of which Israel’s antimissile defenses have thwarted. Israel has also launched thousands of strikes on Lebanon in that period. Over 150,000 people have fled border towns in both countries, with little prospect of returning home.

Ron Huldai, the mayor of Tel Aviv, said the city was on heightened alert.

“The war is still here, and it is hard and painful,” he said on social media, referring to Israel’s war with Hamas in the Gaza Strip.

Matthew Mpoke Bigg, Eric Schmitt, Ronen Bergman and Shuaib Almosawa contributed reporting.

Thinking that maybe an air-conditioning unit had fallen onto it, he and his wife ran out with a fire extinguisher and a hose. They were confused to see so many other onlookers there, too.

“We didn’t understand why the whole neighborhood came out to the streets because of a fallen AC unit,” Mr. Afek said. “But slowly, we began to hear buzz about a drone strike.”

The attack killed at least one person and wounded several others, the authorities said. The body of a 50-year-old man was found in a nearby apartment building as emergency workers combed through the area, Zaki Heller, a spokesman for Israel’s national emergency service, said in a statement. The man was found in his apartment and had shrapnel injuries, according to the Tel Aviv police.

The police described the wounded as “lightly injured.”

By late morning, the glass shards and debris had mostly been cleaned up from the streets.

Holding a roll of tape, Naor Vilner, 32, the manager of a nearby CrossFit studio, was busy taping plastic sheets over its shattered windows.

He recounted hearing a loud explosion from his apartment and tried to go back to sleep. But when he saw a photo sent around in neighborhood WhatsApp groups of a drone’s wing, he determined there had been a strike and went to the studio to inspect the damage.

“Hopefully we’ll be open on Sunday with this behind us,” Mr. Vilner said, “but of course it can’t completely be behind us. It’s a crazy reality.”

Shahar Dubb, 20, a displaced resident from Kiryat Shmona, a town near Israel’s northern border with Lebanon, expressed frustration over people’s reaction to the strike in Tel Aviv.

“I see people in a hubbub, but I ask myself: What’s the uproar?” said Ms. Dubb, who lives with her mother in a cramped hotel room less than a mile from the strike zone. “This happens every day.”

Ms. Dubb’s hometown has been evacuated for nine months and regularly comes under Hezbollah drone and rocket fire.

“People here live in a bubble,” she said of Tel Aviv. “They don’t realize what’s happening in the north.”

But on Friday, a solitary drone slipped through without being shot down or even triggering any warning alerts, killing at least one person and wounding eight others. It was a rare breach in Israel’s vaunted, multilayered aerial defenses, which have allowed Israelis to return to a tense wartime routine, even as the devastating offensive in Gaza has continued.

Israel’s ground-based Iron Dome defense system has generally made short work of Hamas rockets, either shooting down most of them or allowing them to fall in open areas. In mid-April, Israel fired long-range interceptors that took down Iranian ballistic missiles in the outer reaches of the atmosphere, as part of a joint operation with its allies, including the United States.

But drones pose a different kind of threat: Experts say they can be tougher to detect and more difficult to intercept. Rockets and missiles move very quickly at higher altitudes, generating intense heat as they burn fuel, while drones move more slowly at low altitudes, leaving minimal radar or heat signatures. Rockets follow defined trajectories, while guided missiles have limited ability to maneuver, but drones are highly maneuverable.

Iran supplied drones to its militant allies, particularly Hezbollah, the politically powerful Lebanese armed group, and the Houthis. That concerns Israeli military officials, who increasingly anticipate a major battle with Hezbollah, after months of cross-border fire, once the war in Gaza winds down.

“Hezbollah can launch drones with short flight paths that are close to the ground,” said Assaf Orion, a retired Israeli brigadier general. He added, “they’re difficult to detect.”

Close to the Lebanese border, Hezbollah can fire drones at nearby targets quickly enough that there is almost no time for Israeli forces to detect and intercept them, military experts said. Israel’s air defenses have nonetheless managed to knock down scores of drones fired by Hezbollah over the past several months.

But in the event of a full-scale war, Hezbollah could likely launch enough to cause serious damage, despite Israel’s defenses, said Shlomo Brom, a retired Israeli military strategist. In late June, a Hezbollah drone attack wounded 18 Israeli soldiers, one severely, in the northern Golan Heights, the military said.

For months, Israel and the United States have coordinated to intercept the Houthis’ drones and missiles launched at Israel from Yemen. Rear Adm. Daniel Hagari, the Israeli military spokesman, said Friday that most of the Houthi drones have been shot down by an American task force under the U.S. Central Command.

When threatened with drones, Israel generally relies on warplanes to destroy them, using air-to-air missiles, General Orion said. To intercept aircraft arriving from Yemen or Iraq, Israel relies on information from partners like the United States who provide real-time intelligence on threats far beyond the country’s borders, he said.

Admiral Hagari told reporters at a news conference on Friday that Israel’s systems had picked up traces of the drone as it entered. But Israeli officers had failed to identify the craft as a threat, he said.

They both may be right.

Weapons experts say the drone that killed one person and wounded at least eight others appears to be a variant of a Houthi-built, Iranian-designed Samad-3, which was first launched in 2018. At a minimum, they said, it was painted darker to evade air defenses and equipped with a larger fuel tank and engine to give it the range to reach Tel Aviv.

But there is also the possibility that the Houthis outfitted a Samad-3 with materials to evade Israel’s air defenses, as the Yemeni militants try to replicate what Iran is doing to develop stealth drone technology.

Either way, “this was bound to happen,” said Mohammed al-Basha, the Middle East analyst for the Navanti Group, a Virginia-based international research and security company. “The Houthis have been trying since November to have a big hit inside Israel.”

Video of the drone moments before impact, released by the Israeli Defense Forces, as well as pictures of its wreckage show a Samad aircraft that has been at most lightly altered. “It looks pretty ordinary,” said Jeremy Binnie, a weapons analyst and Samad drone expert at Janes, a defense intelligence firm. “It’s possible they have just scaled up.”

He said he saw nothing in the drone’s wreckage to indicate it is a detection-evading stealth aircraft, as a Houthi spokesman claimed.

The dueling accounts left unclear exactly how the drone managed to slip through Israel’s air defenses, among the most sophisticated and powerful in the world.

The Israeli Defense Force spokesman, Rear Adm. Daniel Hagari, said the drone that struck Tel Aviv appeared to be an upgraded Samad-3 with the range to fly from Yemen, and that Israel’s defense systems had apparently picked up the drone but through an “error” failed to register it as a threat.

The Houthi spokesman, Nasruddin Amer, said the drone was an advanced weapon equipped with technologies that made it difficult to detect. He said it was fully manufactured in Yemen and was named Yafa, the Arabic word for Jaffa, the ancient port city that is now part of Tel Aviv.

Mr. Amer said Friday’s strike was a response to what he described as “an escalation in massacres against the Palestinian people in Gaza.”

Named for a former Houthi leader, the original Samad-3 drone had a range of only about 1,120 miles — too little to reach Tel Aviv from Yemen. The Houthis first claimed to have launched it against airports in the United Arab Emirates in 2018, and a U.N. panel of experts concluded the Samad-3 was among the drones that attacked Saudi oil fields in 2019.

Mr. Binnie said Iran began using the Samad-3 around 2020, and the Houthis formally revealed its existence in March 2021. “Certainly the design comes from Iran,” he said. “But there does seem to be some evidence that they are at least partially produced in Yemen.”

Another weapons expert, Ibrahim Jalal, at the Carnegie Endowment’s Middle East Center, said that the drone used in Friday’s attack appears to have been a modified Samad-3, painted darker than the original. But, he said, it might have been built with certain carbon materials that Iran has used in some of its stealth aircraft to enhance radar absorption — a possibility that Mr. Al-Basha echoed.

“If indeed it was not detected, that would be an interesting development — not only for the Houthis, but of course for the whole range of the Iranian axis of resistance, from Hezbollah to others moving forward, because it’s just transferable among them,” Mr. Jalal said.

The Samad-3 is deliberately built as a “low and slow” drone, to make it harder for air defenses to pick it up, said James Patton Rogers, a drone expert at Cornell University. That allows it “to quite literally fly under the radar,” Mr. Rogers said, potentially making it “incredibly hard to spot.”

Or Israeli defenses may have missed the drone simply because of human error, and “contributed to the Houthis achieving a lucky shot,” said Fabian Hinz, an expert at the International Institute for Strategic Studies in London.

Mr. Amer, the Houthi spokesman, said Iran was not involved in the decision to carry out the attack on Tel Aviv. But he said the Houthis briefed the Iranians afterward.

Mr. Jalal raised the possibility that Iran and one of its other proxies, like the Hezbollah forces in Lebanon, may have been involved, given “other incidents where the Houthis would claim, but not necessarily actually conduct, the attack.”

Houthi claims of its weapons or warfare prowess “have to be taken with a grain of salt,” Mr. Jalal said. “They fabricated things in the past, or at least exaggerated.”

Mr. al-Basha said it could have been just “a lucky strike” by the Houthis, but added: “I have learned over the past decade not to underestimate what they claim.”

Eric Schmitt contributed reporting from Washington.

The previous Conservative government had suspended funding after Israel accused a dozen employees of UNRWA of being involved in the Hamas-led attacks that killed about 1,200 Israeli civilians last October. Israel claimed that many other workers at the agency were members of terrorist groups, but has not produced evidence to support those broader charges.

“I was appalled by the allegations that UNRWA staff were involved in the Oct. 7 attacks, but the U.N. took these allegations seriously,” said Mr. Lammy, who was appointed foreign secretary on July 5, a day after the Labour Party’s landslide election victory over the Conservatives.

After an independent review, Mr. Lammy said that Britain had been “reassured” that UNRWA was “strengthening its procedures, including on vetting,” and said the agency was “absolutely central” to ensuring aid reached civilians.

Britain had joined the United States and a dozen other countries in suspending the funding. But the humanitarian situation in Gaza has become ever more dire, and last week 118 countries publicly declared their support for the agency at the United Nations, with the secretary general, Antonio Guterres, declaring, “There is no alternative to UNRWA.”

Mr. Lammy, who recently returned from a visit to Israel, repeated his demand for an immediate cease-fire and criticized Israel over the shortage of aid entering Gaza. “Israel promised a flood of aid back in April but imposes impossible and unacceptable restrictions,” he said. But his statement captured the political pressures that his government is likely to face regarding the conflict.

He did not comment on whether Britain will drop the previous government’s objection to arrest warrants sought by the International Criminal Court for Prime Minister Benjamin Netanyahu of Israel and for the Israeli defense minister, Yoav Gallant.

Mr. Lammy said that he took the issue “extremely seriously,” along with the question of whether Israel was complying with international law. “As soon as I took office, I tasked officials with a comprehensive review of Israel’s compliance with international humanitarian law,” he said, “And that process is now underway.”

Many members of the Labour Party want tougher action against Israel. Some Labour politicians were damaged in the election by the party’s cautious approach to the conflict. Jonathan Ashworth, a Labour figure who would probably have been named to a cabinet post, unexpectedly lost his seat to a pro-Palestinian activist.

Mr. Lammy’s support of UNRWA was widely welcomed in Parliament, though one senior Conservative lawmaker voiced opposition. “UNRWA schools have been repeatedly used by terrorists to both store weapons and launch attacks,” said Richard Holden, a former deputy chairman of the party.

Juliette Touma, an UNRWA spokeswoman, called the decision to resume funding a “very positive and welcome announcement,” adding that the agency “needs every penny as part of its humanitarian response in Gaza.”

She said that UNRWA had no way to verify accusations about the use of its facilities by armed groups but said it had denounced the reports and called for investigations. U.N. investigators are still examining Israel’s accusations that some UNRWA employees participated in the Oct. 7 attacks, she added.

Aaron Boxerman contributed reporting from Jerusalem.

Brian Nelson, under secretary of the Treasury for terrorism and financial intelligence, said in a statement that the new sanctions were intended to undermine the Houthis’ “ability to further destabilize the region and threaten international commerce.”

“Today’s action underscores our focus on disrupting the Houthis’ sprawling network of financial facilitators, shell companies and vessels that enables the primary source of funding for the group’s destabilizing activities,” he said.

The sanctions are being imposed on a far-flung group of individuals and businesses, reflecting the Houthis’ global ties. Among the targeted individuals are a Malaysian and Singaporean national and a Chinese national who the United States said have “facilitated illicit shipments and engaged in money laundering” for the Houthi network.

Commercial shipping companies have been struggling to contend with the effects of the Houthi strikes, which have been rippling across the industry. On Wednesday, the shipping company Maersk said disruptions had extended far beyond the trade routes directly affected by the attacks, which lie between Asia and Europe, with shippers’ forced reroutings leading to congestion, backlogs and delays at ports on alternate routes.

The Houthi attacks have significantly raised shipping costs worldwide. While container costs have not reached pandemic highs, when supply chains were snarled across the globe, the average price to ship a 40-foot container across eight major East-West trade routes has risen more than 285 percent since last year, according to Drewry, a British maritime consultancy that tracks container costs.

The Treasury last month imposed sanctions on Sa’id al-Jamal, identifying him as a Houthi financier based in Iran who directed “a network of front companies and vessels that smuggle Iranian fuel, petroleum products and other commodities to customers throughout the Middle East, Africa and Asia” to fund the Houthis.

On Thursday, the Treasury added sanctions against what it called “seemingly innocuous” companies forming part of the same matrix — including an insurer, an energy trading company and a ship manager, as well as vessels under its management — saying the network continued “to provide tens of millions of dollars in revenue to the Houthis in Yemen.” The designated entities, based in Thailand, Singapore and the United Arab Emirates, operate around the world.

The Houthis on Tuesday released a video that they said showed an attack on a commercial ship in the Red Sea the previous day. The rebel group targeted two vessels on Monday, according to the United States Central Command.

In a post on social media, the Central Command said on Monday that it had destroyed five Houthi drones in the previous 24 hours, citing a rationale repeated across such announcements: that the targets “presented an imminent threat to U.S., coalition forces, and merchant vessels in the region.”

“When I say we are inside of the 10-yard line, we are,” Mr. Blinken said. “We also know that often the last 10 yards are the hardest.”

Speaking at the Aspen Security Forum in Colorado, Mr. Blinken said it was critical not just to secure a deal to free the hostages but also to reach agreement on a postwar plan for Gaza to bring relief to the people there. He said that Hamas could not return to power in Gaza but that Israeli occupation of Gaza could not continue.

“What we can’t have is an agreement that’s followed by some kind of void that will either be filled by Hamas coming back, which is unacceptable, by Israeli prolonging its occupation of Gaza,” Mr. Blinken said. “Or just having a vacuum, filled by lawlessness, filled by chaos, which we see in so many parts of Gaza right now.”

Hamas officials have said they have agreed to cede civil and police control to an independent authority. American officials want security control to be given to a force of Palestinians who support the West Bank-based Palestinian Authority. Hamas has said it will not give up control of its security forces.

Pressure is intensifying on Prime Minister Benjamin Netanyahu of Israel to close a deal before his scheduled visit to Washington next week. Families of hostages have rallied across Israel, calling for their release, and world leaders have been steadily pushing for an agreement.

Mr. Blinken said discussions with Mr. Netanyahu next week will center on postwar reconstruction plans. U.S. officials continue to believe it is unlikely a deal will be reached until after Mr. Netanyahu’s visit.

Asked if the hopes of creating an Palestinian state were alive, Mr. Blinken jokingly quoted Senator John McCain of Arizona saying, “it’s always darkest before it goes completely black.” But Mr. Blinken said that hopes for an independent Palestinian state “can’t be” dead.