The footage showed many people with hands and fists raised in celebration and some jumping for joy on the street. Many in the crowd appeared to be filming the event on their own cellphones.

Social media posts and live television footage also showed people taking animals from the residence, including chickens, ducks and rabbits, and some people posing with the animals.

Monsur Ali, a garment worker, said he was among the thousands of people who entered the prime minister’s residence, many of them taking away objects. He grabbed a plate.

“We went there out of anger,” he said. “Nothing is left there.”

Ms. Hasina, 76, was driven out of office by weeks of protests — initially about coveted government jobs and who is entitled to them — that began without conflict but turned deadly when government security forces cracked down. Nearly 300 people are reported to have died in those clashes.

Many in the country also oppose Ms. Hasina’s increasing authoritarianism after 15 years in power.

The country’s army chief confirmed Ms. Hasina’s resignation in a statement to the nation and said an interim government would be formed.

Ms. Hasina had ruled for years through fear. But the protests had swelled to such large numbers, persisting even after days of deadly crackdown, that the demonstrators’ fear of Ms. Hasina did not keep them off the streets. Instead of backing down in the face of a new curfew and other restrictions, the protesters planned a march that would take them straight back into the maw of the security forces.

Their determination carried the risk of another blood bath. What followed instead, from the perspective of the protesters, was victory. Ms. Hasina fled in a helicopter, a crowd stormed her residence and the army announced that, after more than 15 years in power, she had resigned.

In the aftermath, tens of thousands of people, many shaking their fists in celebration, marched through the center of the capital, Dhaka, and what had been shaping up to be another day of street battles turned into a street party.

That atmosphere of jubilation may be short-lived, however. Bangladesh’s politics have long been violent, and the animosities between Ms. Hasina’s party and the opposition are unlikely to fade soon. Before Bangladesh settles into its next chapter, revenge for years of harsh suppression under Ms. Hasina will be on the minds of many.

The sustained protests that convulsed Bangladesh in recent weeks were a backlash against Ms. Hasina’s formula for power: absolute, disconnected and entitled. She cracked down hard, and the resulting challenge to her rule was a crisis largely of her own making, analysts said. The student-led protests started as a peaceful expression of opposition to quotas that reserve sought-after government jobs for specific groups. The violent response by government security forces and vigilantes from Ms. Hasina’s party sent the country to the verge of anarchy.

Ms. Hasina, 76, deployed every force at her service onto the streets, including a feared paramilitary unit whose leaders have in the past faced international sanctions over accusations of torture, extrajudicial killings and forced disappearances.

It has been before. Bangladesh’s army has a history of staging coups and counter coups. But over the past couple decades, the military has taken a less overt role in public affairs, choosing more often to exercise influence from behind the scenes.

Part of that shift has been attributed to Ms. Hasina. Her father, Bangladesh’s first leader, Sheikh Mujibur Rahman, as well as much of her family, was killed in a deadly military coup in 1975. In her time in office, she has stacked its leadership ranks with loyalists, and allowed them access to lucrative government contracts and other businesses.

There are international incentives for the military, as well, which has been a major contributor to United Nations peacekeeping missions that have given it another important side business. Any involvement in a coup would subject the army to criticism — or ostracism — from the United Nations, whose human rights chief responded to the recent killings by calling for restraint and accountability from those with “command responsibility.”

While the army was deployed on the streets during the crackdown to clear the protesters late last month, there have been reports of discomfort in the ranks over it. Dozens of former senior officers also issued a statement calling on the military not “to rescue those who have created this current situation” — a statement seen by some as referring to the police and paramilitaries, and possibly even to Sheikh Hasina herself.

On Sunday, the army’s chief, Gen. Waker-uz-Zaman, gathered senior officers for a meeting that was seen as an attempt to allay concerns. In a statement after the meeting, the army said its chief had reiterated that “the Bangladesh Army will always stand by the people in the interest of the public and in any need of the state.”

If Ms. Hasina’s power becomes untenable, analysts said the army would be unlikely to opt for a takeover. It might, though, try to aid some transition period from the sidelines with a caretaker government — something that happened in 2007.

“There are major international ramifications to a military coup. And more than leaders it is the younger officers who are hesitant to go ahead with anything of the sort,” said M. N. Khan, a retired general of the Bangladeshi Army.

The exact number of deaths on Sunday was unclear, but it appeared to be the deadliest day since the protests began in July. At least 13 of the dead were police officers, the country’s Police Headquarters said in a statement.

Over the weekend, the tensions flared into the kind of localized clashes across the country that appeared difficult to contain. With the public already angry at the police forces, seeing them as an overzealous extension of Prime Minister Sheikh Hasina’s entrenched authority, attention focused on Bangladesh’s powerful military.

Ms. Hasina has worked to bring the military to heel. But it has a history of staging coups and was being watched for how it positions itself in the escalating crisis.

Here’s what we know about the deadly crackdown on Sunday.

Shayeza Walid contributed reporting from Dhaka.

More than 300 people have been killed. After a curfew and communication blackout eased, the revival of the protests over the weekend, in addition to a call by Ms. Hasina’s party for its own supporters to take to the streets, plunged Bangladesh into a particularly dangerous phase.

On Monday, the army chief announced the resignation and said an interim government would be formed.

Here’s what to know about the protests.

What were the protests about?

Students at the University of Dhaka, the country’s top institution, started the demonstrations on July 1, and they later spread to other elite universities, and then to the general public. The protests turned violent when some members of student wing of the governing party, the Awami League, began attacking the protesters.

Besides sending the police and paramilitaries into the streets, the government locked down schools and colleges. Officials said they slowed down internet connectivity to stop the spread of rumors and protect citizens, making it harder for protesters to organize and make plans via social media platforms.

The protests were initially about coveted government jobs and who is entitled to them. An old quota system, reinstated recently by the courts, reserves more than half of those jobs for various groups, including the families of those who fought for independence from Pakistan. The students said that the system is unfair and that most of the positions should be filled based on merit.

In the past couple of weeks, however, the movement grew massively and become centered on calling for accountability for Ms. Hasina’s increasingly harsh governance.

How did the protests evolve?

The crackdown in late July, which saw over 200 people killed and 10,000 arrested, temporarily dispersed the protesters. However, the large number of deaths also fueled protesters’ anger.

Over the weekend, the tensions spread away from protests and into clashes across the country that appeared difficult to contain. On Saturday at a rally of tens of thousands, protesters called for the resignation of Ms. Hasina, who has been in power for the past 15 years.

In response, Ms. Hasina’s Awami League party called on its supporters to join counter protests, and she asked the country’s people “to curb anarchists with iron hands.”

The threat emboldened protesters, who called for a march on her residence in central Dhaka on Monday. The government once again imposed a curfew, effectively shutting the country down.

By midafternoon Monday in Dhaka, what appeared to be conditions for another deadly day of protests had eased. Police officers let protesters cross barricades into the center of the city, and the army said they would make a statement.

Shortly after, the army chief announced that Ms. Hasina had left the country.

What will happen to Bangladesh after her ouster?

Ms. Hasina was among the world’s longest-serving female heads of government, a secular Muslim who fought Islamic militancy, helped lift millions out of poverty and deftly kept both India and China at her side.

Over the past 15 years, Ms. Hasina entrenched her authority and divided Bangladesh, a nation of 170 million people. Those who were loyal were rewarded with patronage, power and impunity. Dissenters were met with crackdowns, endless legal entanglement and imprisonment.

The army has asked the president, who holds a ceremonial role, to form a new government. Bangladesh’s army has a history of staging coups and counter coups. But over the past couple decades, the military has taken a less overt role in public affairs, choosing more often to exercise influence from behind the scenes.

Over the weekend, the previously private gripes gained a public airing when a major Israeli news network, Channel 12, broadcast accounts of leaked arguments between Mr. Netanyahu and the chiefs of Israel’s foreign and domestic intelligence agencies, Mossad and Shin Bet.

Channel 12 reported that the chiefs accused Mr. Netanyahu of blocking the deal, while the prime minister was said to have accused them of being weak negotiators.

Mr. Netanyahu has blamed Hamas’s intransigence for stalling the negotiations, rather than his own, citing his decision to send negotiators to Cairo over the weekend to continue the talks. But he did not deny private disputes with his security chiefs, complaining only that the leaked reports were themselves harmful to the negotiations.

“The fact is that it is Hamas which is preventing the release of our hostages, and which continues to oppose the outline, and not the government of Israel, which has accepted it,” Mr. Netanyahu told ministers at the start of a cabinet meeting on Sunday. Hamas has repeatedly denied the claim.

There is less debate within the Israeli establishment about the merits of assassinating Ismail Haniyeh, the Hamas leader and top truce negotiator, who was killed in Iran last week.

Mr. Biden’s frustration with Mr. Netanyahu is in part related to the assassination, which the U.S. president said had “not helped” the prospects of a cease-fire agreement.

But among Israeli security officials, the prevailing assessment is that a deal could still be reached within days if Mr. Netanyahu set aside some of his conditions, according to the two Israeli officials who spoke on the condition of anonymity.

To many Israelis, Mr. Haniyeh was seen as a liaison to his more powerful colleagues in Gaza rather than a decision maker in his own right, and he did not have the final say over Hamas’s position on a cease-fire.

Mr. Netanyahu and his supporters argue that Israel should not rush into a cease-fire that could allow Hamas to survive the war intact, and that would also require Israel to release hundreds of Hamas prisoners in exchange for the Israeli hostages seized during the Oct. 7 attack.

The prime minister “deserves special appreciation” for his position, Ariel Kahana, a commentator for Israel Hayom, a leading right-wing newspaper, wrote in a column last week. “Hamas still controls Gaza and so, if the war ends, and certainly if it is reinforced by hundreds of released terrorists, it will immediately begin to regroup militarily,” Mr. Kahana said.

But to his critics, Mr. Netanyahu is holding out for personal reasons rather than patriotic ones.

Mr. Netanyahu’s ruling coalition depends on far-right lawmakers who have said they will leave the coalition if he agrees a deal that would allow Hamas to survive. Since Hamas has rejected a temporary truce, Mr. Netanyahu must therefore choose between a deal and the stability of his government.

“If it is left up to Netanyahu, the war will never end,” Sima Kadmon, a critic of the prime minister’s, wrote in a column on Monday.

To ease his predicament, Mr. Netanyahu wants Mr. Biden to provide a written guarantee that he would support an Israeli resumption of fighting if Hamas reneged on its cease-fire commitments, according to the two Israeli officials. The hope is that such a side-agreement would enable Mr. Netanyahu to convince his coalition partners that a cease-fire might be temporary, potentially allowing him to keep his coalition together.

If Mr. Netanyahu’s government collapses, Israel would likely face early elections that Mr. Netanyahu would struggle to win, according to most polling since late last year. And losing office would heighten his political and legal vulnerabilities: He is currently standing trial on corruption on charges that he has denied.

One U.S. official, speaking on the condition of anonymity to discuss sensitive diplomacy, declined to comment on the idea of Mr. Biden providing a written guarantee. But the official said that a draft of the cease-fire deal already contained safeguards that would allow Israel to walk away from the truce if Hamas broke its terms.

Israel’s military leadership lacks Mr. Netanyahu’s political considerations and has privately determined that a hostage deal must be finalized as soon as possible in order to save the hostages’ lives. While the military has rescued some hostages through raids and rescue operations, top generals concluded weeks ago that further military action to free them may run the risk of killing the others.

More than 100 Israelis, both dead and alive, remain in Gaza, and at least 30 would be released within weeks under the likely terms of a cease-fire deal.

Military leaders also want to focus their energy, resources and troops on Israel’s border with Lebanon, instead of on Gaza. The likelihood of an all-out war with Hezbollah, a Lebanese militia, rose sharply last month after a deadly strike from Lebanon killed 12 children and teenagers, leading Israel to assassinate a top Hezbollah commander.

On Monday, Israelis were braced for aggressive retaliation from Hezbollah, which many fear will prompt a broader war, particularly with Iran, Hezbollah’s benefactor, also poised to strike Israel in response to Mr. Haniyeh’s assassination.

Mediators hope that a truce in Gaza would prompt a similar cease-fire in Lebanon. Hezbollah has said it will keep firing as long as the Gaza war continues.

Myra Noveck and Johnatan Reiss contributed reporting from Jerusalem, and Peter Baker from Washington.

Initial reports were that at least five people were injured in Monday’s attack and that the wounded included both U.S. troops and contractors.

The attack comes as tensions are running especially high in the region, with Israel and its American, European and regional allies bracing for a reprisal attack from Iran in response to the killings last week of a Hamas leader, Ismail Haniyeh, in Tehran, and a Hezbollah leader, Fuad Shukr, in the southern suburbs of Beirut.

Israel has said it carried out the attack on Mr. Shukr but has said nothing about the one in Iran. Iranian officials and Hamas have said that Israel was responsible for Mr. Haniyeh’s killing.

The Iranian government has said that any retaliatory attack will also involve its proxy forces, which include Hezbollah, the Houthis in Yemen and militants in Iraq.

Those Iraqi militants have typically attacked U.S. forces in Iraq and Syria and targeted Israel using longer-range rockets. The region has been on high alert for a broad onslaught, similar to Iran’s attack on Israel in April, which was in response to Israel’s killing of three senior leaders of Iran’s Revolutionary Guards Corps and four other Revolutionary Guard officers in Damascus, Syria.

It was not clear if the rocket attack on Monday at Al Asad Air Base was part of that response or a continuation of ongoing efforts by the Iran-backed groups in Iraq to target U.S. forces, who are stationed in the country at the invitation of the Iraqi government. The chief goal of Iran-backed groups in Iraq is to force the U.S. troops to leave the country entirely. No group has taken responsibility for Monday’s attack.

There is continuing negotiation between senior defense officials in Iraq and the Pentagon over how to reconfigure and downsize the U.S. and multinational forces, but they have not yet reached a decision. Within the Iraqi government, there is division, with factions close to Iran pushing for a speedy U.S. departure while others, including many Iraqi defense officials, are pushing for limited longer-term U.S. involvement.

There are about 2,500 American troops in Iraq, as well as 900 in Syria, where the Islamic State has once again become active.

The White House said in a statement that President Biden and Vice President Kamala D. Harris had been briefed on the attack and had discussed steps that the administration would take “to defend our forces and respond to any attack against our personnel in a manner and place of our choosing.”

After a July 16 drone attack on the U.S. area of the Ain al Asad base, which did not result in injuries, the U.S. military bombed a small drone factory in Jurf al Sakhar, an area south of Baghdad, which serves as a base for the Iranian-backed group Kata’ib Hezbollah and others. The U.S. attack killed four fighters — three Iraqis and a Houthi commander — at the site.

With 13,000 staff members in the embattled territory, UNRWA has been key to efforts to provide shelter, food and other basic services to Gazans during nine months of war that has displaced most of the territory’s 2.2 million people. Tens of thousands have been killed, according to Gaza’s health authorities.

In recent months, most donor nations have resumed funding for the agency, citing its critical role in delivering aid to desperate Gazans, as well as the results of a separate U.N. investigation into UNRWA’s adherence to U.N. neutrality rules that was released in April. But one of its biggest funders, the United States, has not done so. U.S. lawmakers in March blocked all donations for one year.

In a statement on Monday, the agency’s head, Philippe Lazzarini, acknowledged the investigators’ findings and said that the nine employees who were deemed to have possibly participated in the attack “cannot work for UNRWA.”

“I reiterate UNRWA’s condemnation of the 7 October attack in the strongest possible terms,” he said.

The Israeli ambassador to the United Nations, Gilad Erdan, dismissed the report as “a disgrace,” calling it “too little and too late.” In a post on social media, Mr. Erdan accused the investigators of ignoring evidence Israel had provided and called for the agency to be shut down.

Mr. Lazzarini said the agency’s priority was to “continue lifesaving and critical services” for Palestinian refugees in Gaza and elsewhere in the Middle East, “especially in the face of the ongoing war, the instability and risk of regional escalation.”

Israel initially accused 12 UNRWA workers of involvement in the Oct. 7 attack, in which about 1,200 people were killed. In later months, seven other cases were added.

The investigation found no evidence against one of those employees and insufficient evidence against nine others, the U.N. said on Monday.

The Israeli accusations came against the backdrop of decades of friction with UNRWA, which the United Nations General Assembly created in 1949 to care for those displaced in the war surrounding Israel’s creation. More than 700,000 Palestinian Arabs fled or were forced from their homes in what became Israel, and the agency grants refugee status to them and their descendants, who now number nearly six million.

Although it has no official role in resolving the refugees’ plight, Palestinians have long seen it as their protector, and as proof that world powers remain invested in their fate.

Many Israelis, however, argue that the agency perpetuates the conflict by encouraging the belief in a Palestinian “right of return” to what is now Israel. That, critics say, would amount to a demographic threat that would destroy the Jewish state.

In addition to its accusations against individual staff members, Israeli officials have charged that UNRWA in Gaza has been deeply infiltrated by members of Hamas and other militant groups, an allegation agency officials deny.

The investigation whose results were released on Monday did not examine that broader issue, only looking into the allegations of involvement by individual employees in the Oct. 7 attack.

The earlier investigation, whose results were released in April, found that UNRWA had strong protocols for ensuring its neutrality but made a range of recommendations for how it could do better.

Mr. Biden also telephoned with King Abdullah II of Jordan, a day after the Jordanian foreign minister, Ayman Safadi, traveled to Tehran for meetings with his Iranian counterpart. Jordan is a close Western ally and helped intercept Iranian missiles and drones in April during tit-for-tat attacks between Iran and Israel.

“Escalation is in no one’s interest,” Matthew Miller, the State Department spokesman, told reporters in a briefing on Monday. He added that the United States doesn’t consider escalation “inevitable” and is sending messages to Iran through its allies in the region that an attack would not serve Iranian interests, or the region’s.

“The leaders discussed their efforts to de-escalate regional tensions, including through an immediate cease-fire and hostage release deal,” a White House description of the call said.

Egypt’s foreign minister, Badr Abdelatty, spoke on the telephone with the American secretary of state, Antony J. Blinken, urging him to pressure Israel to “seriously engage” in cease-fire talks, the Egyptian foreign ministry said in a statement, according to Reuters news agency.

The Israeli prime minister, Benjamin Netanyahu, has come under fire from President Biden, publicly, and from senior leaders in Israel’s military and intelligence circles, privately, for failing to make concessions to reach a cease-fire agreement. Mr. Netanyahu has blamed Hamas, however, for the stalled talks.

The Egyptian statement came on a day when Mr. Adbelatty met with the Turkish foreign minister, Hakan Fidan, in Cairo to talk about the war in Gaza and efforts to halt a regional escalation.

Mr. Miller said that from the perspective of the United States, reaching a cease-fire agreement in Gaza is the best way to defuse the explosive tensions in the Middle East, and on Monday urged Israel and Hamas to “get to yes.”

On Wednesday, Foreign ministers from Islamic countries will meet in Saudi Arabia for an extraordinary meeting of the Organization of Islamic Cooperation that was called to discuss “the continued crimes of the Israeli occupation against the Palestinian people,” including Mr. Haniyeh’s assassination, the organization said in a statement.

Iran requested the meeting, according to the country’s foreign ministry spokesman, Nasser Kanaani. During a news conference in Tehran, Mr. Kanaani blamed Israel as the source of the escalating tensions in the region, according to the state-affiliated Iranian Students’ News Agency.

Israel has not confirmed or denied that it was behind Mr. Haniyeh’s assassination, which came less than a day after an Israeli strike killed a senior commander for Hezbollah, an Iran-backed militia in Lebanon, in a suburb of Beirut.

Prime Minister Benjamin Netanyahu of Israel said on Sunday that his country was engaged in “a multi-front war against Iran’s axis of evil,” and that it would “exact a heavy price for any act of aggression against us, from whatever quarter.”

But already, there are signs that the killing of Mr. Haniyeh — and fears of the retaliatory violence it could unleash — could push Gulf governments closer to Iran and further from Israel as they seek to de-escalate tensions that threaten their own security.

On Friday, Anwar Gargash, a senior adviser to the ruler of the United Arab Emirates, expressed his condolences to Mr. Haniyeh’s family members in a social media post, and thanked neighboring Qatar for hosting his funeral — an unusual statement from a government that despises Hamas and led a diplomatic push for Arab countries to establish relations with Israel.

“The Emirates rejects all forms of political violence and assassination,” Mr. Gargash wrote, adding that “there is no path to stability except through justice, wisdom and dialogue.”

Saudi Arabia re-established relations with Iran, its regional rival, last year, citing a desire to open direct channels of communication and reduce political tensions. The meeting of Islamic foreign ministers scheduled for Wednesday in Jeddah could showcase that trend, particularly if Iran and other countries in attendance issue a shared statement rebuking Israel.

Michael D. Shear and Ephrat Livni contributed reporting in Washington, D.C.

Mr. Shoigu’s visit underscores the close alliance between Iran and Russia, which has strengthened since the war in Ukraine started in 2022. Iran has provided Russia with military drones, and the two countries recently finalized an agreement to expand their military and intelligence cooperation.

Iranian media reported that Iran has requested advanced air-defense systems from Russia as it prepares for a possible war with Israel.

Two Iranian officials familiar with the war planning, one a member of the Revolutionary Guards Corps, confirmed that Iran has made the request and said Russia has started delivering advanced radars and air-defense equipment. The officials spoke on the condition of anonymity because they were not authorized to discuss the aid publicly.

Iran’s supreme leader, Ayatollah Ali Khamenei, ordered a direct strike from Iran on Israel after the Hamas political leader, Ismail Haniyeh, was killed in an explosion at his guesthouse while he was visiting Iran for the new president’s inauguration.

American and Israeli officials have said that they expect Iran and its allied militant groups in the region to launch a large and coordinated attack on Israel. The groups, known as the “axis of resistance,” include Hezbollah in Lebanon and the Houthis in Yemen.

Iranian state television showed Mr. Shoigu and General Bagheri greeting each other, meeting one-on-one, then attending a larger meeting at a conference table with members of the Russian delegation and Iranian military officials.

“We are ready for full cooperation with Iran on regional issues,” Mr. Shoigu said, according to Iran’s state media.

General Bagheri told Mr. Shoigu that the relationship between their nations was “deep, long term and strategic,” and would only expand under Iran’s new government, according to Iranian media reports.

Even though Russia also has economic and cultural ties to Israel — a large number of Russian Jews live in Israel — analysts say that Russia can’t afford to turn down Iran’s requests for help, because it relies heavily on Iranian drones in Ukraine.

“If Iranians are asking Russians for air defense, they are cashing in their chips,” said Colin P. Clarke, director of policy and research at the Soufan Group, an intelligence and security consultancy. “The question is how do Russians assuage Tehran without ruining their relationship with Israel.”