“Nobody I know has prepared for a possible war. We are jarred, let us have our normal life. We are not willing or want to enter a war era,” Mahdieh, a 41-year-old engineer in Tehran, said in a phone interview. She asked her last name not be published out of fear of retribution. She said she and her husband had prepared an emergency bag with their documents in case they needed to leave Tehran.

A viral message shared on social media by many Iranians read, “NO WAR,” and “Which bunkers will you use to shield the people? How will you repair damaged infrastructure? There is no good in war, do not lay ruin to Iran.”

On Monday Iran launched 180 ballistic missiles into Israel in retaliation for Israel’s killing of its top regional ally, the Hezbollah leader, Hassan Nasrallah, that of a senior Iranian general in Beirut and that of the political leader of Hamas in Tehran. Israel has said it plans to respond by attacking Iran; its potential targets include military bases for the Revolutionary Guards Corps and oil refineries.

Iran’s President Masoud Pezeshkian traveled to Qatar on Wednesday to attend a conference of the Organization of Islamic Countries, where he said that Iran did not seek war, saying “there are no winners in war, we know this.” And then he warned, “Iran will respond stronger if Israel makes the slightest mistake.”

Iran’s mission to the United Nations said in a statement that Tehran and Washington had exchanged messages through their official intermediary in Tehran in the aftermath of the attack on Israel. The statement said that Iran considered any country that assisted Israel in an attack on Iran “an accomplice and a legitimate target.”

According to two Iranian officials, who are familiar with the war planning and were not authorized to speak publicly, Iran had asked Russia for cooperation with satellite intelligence ahead of an Israeli strike.

But despite the official saber rattling, even some supporters of the government who had cheered the attacks on Israel were now confronting the realities of an all-out war that could take out infrastructure and harm the economy. Facing that possibility, some said they hoped Israel’s response would be limited and any tit-for-tat strikes would end quickly.

“We had to slap it [Israel] in the face, otherwise it would keep moving forward,” said Hamidreza Jalaeipour, a prominent sociologist close to the reformist faction, in a discussion on the application Clubhouse. “If there is a war, it will be imposed on us.”

Mr. Jalaeipour said he predicted that in the event of war the majority of Iranians would rally behind the flag to defend their country forcefully and put divisions aside.

But discontent against the government runs deep, and in waves of protests, notably in the women-led uprising in 2022, demonstrators called for the toppling of the ruling clerics. The loyalty and ideological fervor of the early years of the revolution — when even teenagers volunteered for the front lines of the eight-year war the country was then fighting with Iraq — has given way to despair and frustration with the status quo.

Some opponents of the government said they were angry that Iran had struck Israel in the first place, placing the lives and safety of its own citizens at risk for a cause outside its own borders. In anti-government protests in previous years, people have chanted, “No to Gaza, No to Lebanon, my life for Iran.”

And now that Israeli attacks seemed likely and imminent, the government had not announced any emergency provisions to prepare the population for war.

“Most of us are not happy about the interference of the Islamic Republic in the region and its so-called proxies. People do not want their national resources to be spent abroad,” said Mahan, a 50-year-old doctor in the northern city of Rasht. “The most pressing feeling these days, both for myself and the majority of friends and people I know, is the fear and worry of war.”

He said that she had endured significant trauma over a long period, including rape and abuse. She received food and basic treatment in Israel, he said, and U.S. officials then escorted her to Jordan by car, from which she was returned to her family in Iraq. An Israeli diplomat, David Saranga, posted a video on social media showing Ms. Sido’s return, and said her captor was “a Palestinian Hamas-ISIS member.” The New York Times has not verified the video.

Ms. Sido and her family could not be contacted for comment.

General Goren said that the Israeli military had learned about her situation based on intelligence, and that the Israeli authorities engaged the United States for more information. Israel and the United States then began planning the operation, which added the cooperation of Jordan, and other unnamed international partners, he said.

Ms. Sido was sold by an ISIS operative more than 10 years ago to a member of Hamas who took her to the Gaza Strip, possibly through the Rafah crossing at the Egyptian border, General Goren said. That timing suggests she was initially captured when ISIS overran northern Iraq in 2014 and carried out what the United Nations has deemed a genocide against the Yazidi, an ethno-religious minority.

Her captor in Gaza was killed, General Goren said, likely by an Israeli airstrike, and Ms. Sido fled and hid. He did not specify when that occurred, but said that it was at that point that the Israeli authorities learned of her existence, confirmed it with Americans and planned the rescue operation. She was taken out of Gaza through the Kerem Shalom crossing, another entry point at Gaza’s southern border.

The Yazidis were targeted by the Islamic State, or ISIS, in August 2014, when ISIS captured about one-third of northern Iraq and large swaths of territory in neighboring Syria. Up to 10,000 Yazidis were killed; about 400,000 were displaced from their homes in Iraq’s remote, mountainous Sinjar district; and more than 6,000 were enslaved, most of them women and children, according to Yazda, a nonprofit group created in the wake of the onslaught to aid Yazidis.

Many of the enslaved Yazidis were sold in slave markets in Syrian cities, according to the Norwegian Refugee Council, a humanitarian agency.

In 2015, Sinjar was captured from ISIS by Kurdish forces and Yazidi fighters with the backing of American air power.

Rawan Sheikh Ahmad contributed reporting.

The attempted assassination was the latest move by Israel in its quest to steadily decapitate much of Hezbollah’s leadership. It followed Israel’s invasion of southern Lebanon earlier this week.

Here’s what we know about Mr. Safieddine.

Born in the early 1960s in southern Lebanon, Mr. Safieddine was one of Hezbollah’s earliest members. He joined after the Shiite Muslim group was formed in the 1980s, with Iranian guidance, during Lebanon’s long civil war. He rose quickly up its ranks alongside Mr. Nasrallah, playing many roles and serving as a political, spiritual and cultural leader, as well as leading the group’s military activities at one point.

As Mr. Nasrallah did, Mr. Safeiddine usually appeared in a black turban, marking him as a revered Shiite cleric who could trace his ancestry back to the Prophet Muhammad.

Biographical information reported in various outlets across the Middle East and Turkey portrays a rapid rise through Hezbhollah’s ranks. In 1995, he was promoted to Hezbollah’s highest council, its governing Consultative Assembly, and was soon after appointed as head of the group’s Jihadi Council, which controls Hezbollah’s military activities. Just three years later, in 1998, Mr. Safieddine, was elected to lead the party’s Executive Council, a position that was also twice held by Mr. Nasrallah, including before his appointment as Hezbollah’s secretary-general in 1992, the report said.

Like Mr. Nasrallah, he studied in Iran. Mr. Safieddine formed strong ties with Tehran during his religious studies in the Iranian city of Qom before returning to Lebanon to work for Hezbollah.

Those ties are also deeply personal. He was close friends of Maj. Gen. Qassim Suleimani, an Iranian who commanded the Islamic Revolutionary Guards Corps’ Quds Force until the United States killed him in an airstrike in Baghdad in 2020.

Later that year, Mr. Safieddine’s son Reza Hashem Safieddine married the Iranian general’s daughter, Zeinab Suleimani, in a much-publicized wedding. The marriage was seen by some analysts and critics as emblematic of Iran’s entrenchment in Hezbollah. The U.S. Treasury Department has described Mr. Safieddine’s brother, Abdallah Safieddine, as Hezbollah’s representative to Iran.

Mr. Safieddine was designated a terrorist by the United States and Saudi Arabia in May 2017 for his leadership role in Hezbollah. At the time, the State Department called him “a senior leader” in Hezbollah’s Executive Council, which oversees the group’s “political, organizational, social, and educational activities.” It said that Mr. Safieddine posed “a serious risk of committing acts of terrorism that threaten the national security and foreign policy of the United States.”

The United States designated Hezbollah a terrorist organization in 1997 and holds the group responsible for multiple attacks that killed hundreds of Americans, including the suicide truck bombings of the U.S. Embassy and U.S. Marine barracks in Beirut in 1983, the U.S. Embassy annex in Beirut in 1984 and the 1985 hijacking of TWA flight 847.

Farnaz Fassihi contributed reporting.

The strike was a sign that Israel had not let up on its campaign to eliminate the leadership of the Iranian-backed group, nearly a week after Mr. Nasrallah was killed.

Mr. Safieddine, Mr. Nasrallah’s cousin, is in his 50s and has long been a major player in Hezbollah and has been considered a contender to become the group’s new secretary general. Israeli officials previously told The New York Times that Mr. Safieddine was one of the few senior Hezbollah leaders not present at the site of Israel’s heavy bombardment last Friday near Beirut that killed Mr. Nasrallah.

It was not immediately clear if Mr. Safieddine was present in the bunker struck overnight Friday.

The Israeli military did not immediately respond to a request for comment about the strike, but had issued an evacuation order for the Burj al-Barajneh neighborhood in southern Beirut late on Thursday night. Shortly afterward, around midnight, a series of huge explosions rocked the Dahiya, the densely populated neighborhoods just south of Beirut where Mr. Nasrallah was killed and Hezbollah holds sway.

The shock waves sounded across the Lebanese capital, shaking buildings; they were felt at least 15 miles away. It was one of the heaviest bombardments in the area since the war began last October, according to Lebanon’s state-run news agency.

Who is Hashem Safieddine?

Born in the early 1960s in southern Lebanon, Mr. Safieddine was one of Hezbollah’s earliest members after the Shiite Muslim group was formed in the 1980s, with Iranian guidance, during Lebanon’s long civil war.

He rose quickly up its ranks alongside Mr. Nasrallah, playing many roles and serving as a political, spiritual and cultural leader, as well as leading the group’s military activities.

Mr. Safieddine has strong ties with Tehran, formed during his religious studies in the Iranian city of Qom. Like Mr. Nasrallah, he studied in Iran before returning to Lebanon to work for Hezbollah.

A cleric, Mr. Safieddine was designated a terrorist by the United States and Saudi Arabia in May 2017 for his leadership role in Hezbollah. At the time, the State Department called him “a senior leader” in Hezbollah’s executive council, which oversees the group’s political, organizational, social and educational activities.

Which other Hezbollah leaders has Israel targeted?

The strike targeting Mr. Safieddine was the latest in a series of successful Israeli attacks in Lebanon seeking to kill Hezbollah’s leaders.

On Thursday, an Israeli strike targeted the Hezbollah commander Rashid Shafti, the group’s official in charge of telecommunications and computer division in Beirut, according to two Israeli officials. Mr. Shafti had lost fingers in the wave of electronic explosion attacks Israel carried out this month, they added.

The Israel Defense Forces said in a statement on Thursday that it had also killed Mahmoud Yusef Anisi, a Hezbollah official it said had been involved in the group’s precision-guided missile manufacturing chain in Lebanon.

In the strike that killed Mr. Nasrallah last week, several of the group’s leaders were also slain, including Ali Karaki, Hezbollah’s top commander in southern Lebanon.

Ibrahim Aqeel, who oversaw Hezbollah’s military operations and founded the group’s elite commando unit, was killed on Sept. 20.

Euan Ward contributed to reporting.

The Israeli military said in a statement early Thursday that it had killed the head of Hamas in Tulkarm, Zahi Yaser Abd al-Razeq Oufi, “alongside additional terrorists.” It said he had planned and led multiple “significant” shooting attacks and car bombings on Israeli civilians in the West Bank and had supplied weapons to other operatives who also carried out attacks on Israelis.

The Israeli airstrike was aimed at a popular cafe in Tulkarm, according to Wafa news agency, killing a family in an adjacent house and children and older people in the neighborhood.

Tulkarm has been the focus of recent Israeli military raids in the West Bank, which have destroyed the city’s infrastructure and businesses.

Suleiman Zuhairi, a former Palestinian deputy minister who lives on the outskirts of Tulkarm, said Israel had not carried out such a bombardment in the West Bank for years, if not decades.

“The blast was terrifying,” he said. “My house trembled from the shock wave,” he continued, though it was a distance from the reported blast site.

Mr.Zuhairi said that with Israel’s assault on Lebanon drawing international attention, and its continuing war in Gaza doing so to a lesser extent, Israel was operating with a free hand to escalate its campaign in the West Bank.

Aaron Boxerman reported from Jerusalem and Ephrat Livni from New York.

The Israeli assaults on Wednesday included a series of strikes on several school buildings and homes across Gaza and on an orphanage sheltering displaced civilians, local officials said. The local office of the United Nations human rights agency sharply condemned the strikes in a statement on Thursday, saying that Israel was “destroying the only viable shelters remaining for the more than one million Palestinians who have been forcibly displaced” and that such attacks had become “an almost daily event.”

At least eight more people were killed near Gaza City by Israeli bombardment of the orphanage building, which is owned by Al-Amal Institute for Orphans, where hundreds of displaced civilians were sheltering, the institute said in a statement on Wednesday. A majority of those residing in the building, which was heavily damaged by the attack, were women and children, the institute said.

The Israeli military also said it had bombed four school buildings in Gaza on Wednesday. Those strikes killed at least 17 people east of Gaza City, and at least five people at a school sheltering displaced people in Nuseirat, in central Gaza, the Palestinian Civil Defense said.

The Israeli military did not respond to questions about the locations of the other two schools. The military said, without providing evidence, that all four schools were being used as Hamas command and control centers, a claim it has repeatedly made to justify increasingly frequent strikes on Gaza school buildings where displaced people take refuge.

The strikes came days after Action on Armed Violence, an advocacy group that focuses on the effect that conflict has on civilians, said in a new analysis that, on average, explosive Israeli weapons had hit civilian infrastructure in Gaza every three hours since the war began.

The attacks have brought the death toll in Gaza to at least 41,788 people since Oct. 7, according to the local health ministry. Experts have said the true total is likely far higher.

Oil prices rose more than 4 percent on Thursday, with Brent crude, the global benchmark, climbing above $77 a barrel for the first time in a month after Mr. Biden’s remarks. Before the missile attack, Brent was trading at just above $71 a barrel.

Prime Minister Benjamin Netanyahu of Israel said after Iran’s attack on Tuesday that Tehran had “made a big mistake — and it will pay for it.”

When asked if he would allow Israel to retaliate against Iran, which said it had launched the missiles in retaliation for the assassinations of leaders of Hamas and Hezbollah, its proxies, Mr. Biden said: “First of all, we don’t ‘allow’ Israel. We advise Israel. And there is nothing going to happen today.”

Iran is a major oil producer, pumping about two million barrels a day, or about 2 percent of the world’s supply. Its production and sales are hampered by international sanctions, and most of its exports are bought by China.

The intensifying fighting between Israel and Iran and Iranian-backed groups, especially Hezbollah in Lebanon, has pushed up oil prices this week. The main concern is that the escalating conflict could prompt Tehran to try to restrict the flow of oil from key exporters like Saudi Arabia and the United Arab Emirates.

Prices haven’t climbed back to their peaks this year, however, because those worries have been largely outweighed by factors like weak energy demand in China and increased oil production in the United States and elsewhere.

An agreement reached in June by Saudi Arabia and seven other oil producers to begin unwinding some production cuts also continues to weigh on prices. While these increases were recently postponed, the anticipation of increased supplies coming onto the market has offset some of the worry about potential outages stemming from fighting between Iran and Israel.

Until recently, oil prices had been steadily drifting lower, down from about $90 a barrel six months ago.

Mr. Ammar’s building — in the Bachoura neighborhood of Beirut, Lebanon’s capital — had housed apartments and the offices of rescue workers from a Hezbollah-affiliated civil defense group.

The strike, one of Israel’s latest attacks targeting the militant group and political organization Hezbollah, killed nine rescue workers and injured 14 other people, according to the Lebanese Health Ministry.

“They are civilian rescuers, who are helping in rescue operations,” Mr. Ammar said, referring to the workers that had occupied the building. “They are helping civilians from different sects.”

The attack in Bachoura added to Israel’s recent expansion of its bombing campaign against Hezbollah in Lebanon. Israel and Hezbollah have been exchanging rocket fire since the Lebanese group began firing rockets into Israel on Oct. 8 in solidarity with its ally Hamas in Gaza. Those confrontations were mostly limited to the Israel-Lebanon border.

But this month, the Israeli military assassinated Hezbollah’s leader in a neighborhood south of the capital, then earlier this week struck a neighborhood of Beirut in what appeared to be its first attack in the city limits since 2006. Thursday’s strike in Bachoura again brought the fighting to the heart of Lebanon’s capital, landing several hundred yards from the country’s Parliament and some Western embassies.

The Israeli military said in a statement just before midnight on Wednesday that it was conducting a “precise strike” in Beirut, but did not immediately respond to a request for comment on the attack.

“I don’t feel safe in Beirut anymore,” Mr. Ammar said. “This is a destructive war.”

On Thursday afternoon, other residents of the building who had evacuated after the strike returned to assess the damage. Iman Chamseddine stood on the sidewalk outside the building with her three nieces, watching a bulldozer remove the rubble.

Ms. Chamseddine, 65, lives in southern Lebanon, she said, but fled to Beirut last week as Israeli missiles rained down on the area near her home. She was staying at her brother’s apartment in the building when the airstrikes hit.

“I can’t describe these moments,” Ms. Chamseddine said.

“This is not a stroll in the park,” said Miri Eisin, a retired Israeli army colonel who is now a fellow at Israel’s International Institute for Counter-Terrorism. “This is going to be hard, just like it was hard against Hamas.”

The focus of the operation, the Israeli military has said, is to eliminate Hezbollah tunnels, weapons caches and rocket-launching infrastructure that have been a persistent threat to Israel’s northern areas. The Iran-backed militia started targeting northern Israel more intensively with rocket and missile fire a year ago, in solidarity with Hamas after its Oct. 7 attacks prompted Israel to go to war in Gaza.

The Israeli military has been vague on the numbers of troops it has sent to join the operation in Lebanon, citing operational security. Three of the divisions are usually based in northern Israel, and recently they have been joined by two others that fought in Gaza over the past year. Those divisions were tasked with finding and destroying Hamas tunnels and weapons caches in densely populated Gaza, Colonel Eisin said.

The area of southern Lebanon where the Israeli forces have been deployed is much bigger than Gaza, and the rugged terrain more difficult to navigate, posing more complications, she said.

Soldiers in Lebanon could contend with subterranean tunnels under towns and villages, connected to houses and buildings with deep shafts, and the threat of booby traps.

Over the past year, Israeli military officials said, teams of commandos staged dozens of brief raids into Lebanon to target Hezbollah infrastructure near the border, but covert operations only go so far, Colonel Eisin said. “To get the rest, you move to the overt stage, which is where we are now,” she said.

But Hezbollah fighters are better armed and trained than Hamas, which will make for a far more difficult fight. On Wednesday, the Israeli military said that eight of its soldiers had been killed in the first day and a half of combat in Lebanon, a relatively high toll compared with the daily losses the military has taken in the war in Gaza. The Israeli military gave few details of how the soldiers had died, but had earlier said they were engaged in “close-range” fighting.

Hezbollah’s forces have taken a beating from repeated Israeli strikes over the past month. But it has long been able to rearm itself by smuggling weapons across the porous Lebanese border with Syria, an ally of Iran.

Hezbollah is also more experienced, having spent the past decade fighting in the Syrian civil war. And then there is the terrain: high hills and steep gullies that tax an infantry force far more quickly than the comparatively flat land of Gaza. For Israeli military planners, sending additional troops to the Lebanese border is about “making sure we get the job done,” Colonel Eisin said.

Gabby Sobelman, Natan Odenheimer and Aaron Boxerman contributed reporting.

The warning was posted online by Avichay Adraee, an Israeli military spokesman, who told residents that “for your own safety you must evacuate your homes immediately and head north of the Awali River.”

“Save your lives,” Mr. Adraee said. “Anyone who is near Hezbollah elements, installations and combat equipment is putting his life at risk. Any house used by Hezbollah for its military needs is expected to be targeted.”

The Israeli military said it had killed the 15 fighters on Thursday in an airstrike on a local government office in Bint Jbeil, a large town near the border with Israel. It said the office was being used to store “large quantities of Hezbollah weapons.”

Israel also struck overnight in and around Beirut, the capital, including a direct hit on a health authority building in the central Bachoura neighborhood that killed at least nine people and injured 14 others, according to Lebanon’s health ministry.

Hezbollah continued to attempt aerial attacks on northern Israel on Thursday, but appeared to have caused no damage. The Israeli military said several dozen “projectiles” had been fired from Lebanon into northern Israel, setting off air-raid sirens deep into the heavily populated Galilee. Some of the projectiles were intercepted, while others struck empty areas, it said.

Likewise, Yemen’s Houthi militia, an Iran-backed group allied with Hezbollah that has frequently targeted central Israel, boasted of an attempted attack on southern Tel Aviv on Thursday morning. The Houthis hailed the assault, which appeared to have involved drones, as a victory, but Israel said it had intercepted the craft over the sea, and they did not set off air-raid sirens in the city’s south.

The Israeli military also said that it had carried out a series of other strikes across Lebanon’s south on Thursday morning that had “eliminated” an unspecified number of Hezbollah fighters, including some who fired at Israeli soldiers inside Lebanon and others who had fired into northern Israel.

The military did not specify where those clashes had taken place, but Hezbollah said on Thursday that it was fighting Israeli troops in the village of Maroun al-Ras for a second day. The group said in a statement that it had “detonated two explosive devices at dawn” when Israeli soldiers tried to enter the town.

Hezbollah also said it had fired rockets into northern Israel, in and around Misgav Am, an evacuated town in a closed military zone that the group said Israeli soldiers were using as a staging area. The Israeli military said air-raid sirens had sounded throughout the day in that area, but reported no damage.