That was his last day alive. Mr. Jawad, an American citizen, husband and father, and resident of Dearborn, was killed on Tuesday at 9:30 a.m. during an Israeli airstrike, his family said.

“I would often ask him if he was scared, and he repeatedly told me that we should not be scared because he is doing what he loves the most: helping others live in the land he loved the most,” his daughter Nadine Jawad, a Rhodes scholar and Stanford medical school graduate, wrote in the statement.

When Mr. Jawad’s wife was reached on Friday, she said the family declined to comment further.

The airstrike was part of Israel’s intense bombardment and ground invasion in Lebanon, intended to target Hezbollah forces in that country and stop Hezbollah rocket attacks on northern Israel. The military campaign has caused widespread destruction and displacement. At least 1,600 people have been killed by the airstrikes, and over 1.2 million people have been displaced across the country, according to Lebanese authorities.

A State Department representative wrote in a statement on Friday evening that it had confirmed that Mr. Jawad was a U.S. citizen and that it was “aware and alarmed” of reports of his death.

“We extend our condolences to the family,” the statement said.

His friends and family described Mr. Jawad as a man deeply committed to his faith and to helping others, especially through his frequent trips to Lebanon, where he quietly paid off debts of people living there and supported those without the means to flee. He was also known for his devotion to his family — he is survived by his wife and four children — and his passion for soccer.

“He was this old-school, legendary father figure,” said Hussain Makke, 33, a preacher and teacher of Islamic sciences. Mr. Makke said he was living with his parents in London after his home in Lebanon was destroyed.

Mr. Makke stayed with Mr. Jawad’s sister in Dearborn several years ago. Mr. Makke’s father was also friends with Mr. Jawad and completed the hajj, the pilgrimage to Mecca, with him.

Hamzah Raza, another friend of Mr. Jawad’s who is living in Maryland, described him in a statement on social media as someone who loved people and loved helping people.

Mr. Raza, 27, a religious studies Ph.D. student, recalled in his post how, a week before Mr. Raza went to Lebanon, he told Mr. Jawad that he wanted to buy some books there.

Mr. Raza wrote that Mr. Jawad told him, “Just send the names of the books and I will get them for you. I want you to have as much time as you can seeing the country.”

As the fighting between Israel and Hezbollah escalated, so, too, did Mr. Jawad’s efforts to help people in Lebanon, Mr. Makke said.

He added that during a recent series of Israeli airstrikes, Mr. Jawad saved his nephew, who was one of Mr. Makke’s students at a seminary in southern Lebanon. Mr. Jawad’s nephew did not have any family in the area, and Mr. Jawad drove to him and took the nephew to Beirut, perhaps saving his life, Mr. Makke said.

Mr. Makke said that a video taken from that experience shows Mr. Jawad laughing and smiling, even though the two were driving under airstrikes.

“He made it into an action movie,” he said. “He knew how to keep morale high, to not feel scared.”

But while Mr. Jawad also could have flown home, he chose to remain behind: “In his last days, he chose to stay near the main hospital in Nabatieh to help the elderly, disabled, injured and those who simply couldn’t financially afford to flee,” the statement from his family said.

His family noted in the statement that Mr. Jawad’s death was one of many across the Middle East.

“The fact that he was an American citizen should not make his story more important than others,” his daughter wrote.

According to a fund-raiser in Mr. Jawad’s memory, he sent a voice note to his children before his death.

“Peace be upon you,” he told them. “Everything is OK, but if something happens to me, your duty is to the poor.”

Kirsten Noyes and Sheelagh McNeill contributed research.

“These actions were taken to protect freedom of navigation and make international waters safer and more secure for U.S., coalition, and merchant vessels,” the post said.

The Houthi-affiliated al-Masirah TV reported four strikes on Sanaa, the capital of Yemen, seven on the port city of Hodeidah and at least one strike on Dhamar, south of the capital.

The attack on Sanaa came as the Houthis and their supporters were holding their weekly “million-man march” protest, which this week was focused on Israel’s killing of Hezbollah leader Hassan Nasrallah in an airstrike near Beirut, Lebanon, last Friday.

The Houthi-run Yemen News Agency, SABA, reported that Hashem Sharaf al-Din, a Houthi official, said that he considered the strikes “a desperate attempt” to intimidate the Yemeni people and he vowed not to be deterred by them.

But the Houthi attacks on commercial vessels have increasingly drawn the ire of international actors and condemnation by diplomats. The Red Sea is a key trade route between Asia, Europe and the Middle East. Since the strikes began, many vessels have been forced to reroute. Those that have not have sometimes paid severe consequences.

Ships have been hit and sustained damage, and some sailors have been abducted and held captive for many months, while others have died or been injured in the Houthi attacks. In August, a Houthi strike on a Greek oil tanker threatened to devolve into an environmental disaster as the burning ship remained at sea for weeks, with militia members threatening tugboats attempting to salvage the vessel. The ship was towed to safety in mid-September.

The attacks on commercial shipping have been met with counter strikes by the United States military and British troops before. Between January and May, the two countries’ militaries conducted at least five joint strikes against the Houthis in response to the attacks on shipping.

United States Central Command regularly announces actions against the militant group. In August, after the Houthis said they targeted American warships, the U.S. military struck back. Last week, the Houthis made a similar claim, and now appear to have drawn the same response.

The latest strikes by the United States come as tensions in the Middle East have risen significantly following Israel’s killing of Mr. Nasrallah, its expanded operations against Hezbollah in Lebanon and an escalating conflict with Iran, which launched a salvo of about 200 missiles at Israel on Tuesday in retaliation for the assassinations of some of its proxy groups’ leaders.

On Sunday, the Israeli military also struck in Yemen in response to several recent Houthi missile strikes targeting Israel.

What was clear from the twisted mangles of concrete and destroyed buildings across the Hezbollah stronghold of the Dahiya, along with Israel’s widening ground invasion in the south, is that Israel is determined to take the fight against Hezbollah to a new scale. It’s doing so not just in the south, where its ground invasion is seeking to halt Hezbollah’s rocket fire into northern Israel, but also with its systematic targeting of Hezbollah’s remaining leadership, whose movements Israeli intelligence apparently still track.

Many people in Lebanon and the broader Middle East had long feared that such a war was coming, even before the Hamas-led Oct. 7 attacks on Israel. Hezbollah began firing on northern Israel soon after in solidarity with Hamas in Gaza. Hezbollah last fought an inconclusive war with Israel in 2006, and, given Iran’s support for Hezbollah, concern had built over time that they would soon be at war again.

After nearly a year of tit-for-tat strikes, as both groups tested the tolerance of the other side, Israel dramatically escalated the confrontation.

Three weeks ago, Israel detonated thousands of Hezbollah’s pagers and walkie-talkies, killing scores of people and injuring thousands. Last Friday, Mr. Nasrallah was assassinated. And overnight on Thursday came the gigantic attack in which Israel tried to kill Mr. Safeiddine, whose fate remains unclear.

The fighting has now spread far outside of the area along the Lebanon-Israel border where the warring parties initially sought to keep it contained. Israel has sent ground troops tasked with destroying Hezbollah’s military infrastructure into southern Lebanon, its first such invasion since 2006. Nearly a dozen of its soldiers have been killed in clashes there, including two killed in northern Israel that the military announced on Friday.

Israel’s airstrikes — which it says target Hezbollah’s munitions, bases and commanders — regularly kill civilians, bring down buildings and send up huge clouds of smoke in and around Beirut and elsewhere in the country. One strike on Friday left a large crater near a border crossing with Syria, forcing people fleeing from one war-torn country to another to carry their possessions around its rim.

Hezbollah, although battered by Israel’s recent attacks, still fires barrages of rockets over the border, as well as missiles that reach deep inside Israel and send people running for shelters.

Israeli leaders now say they can no longer tolerate the threat that Hezbollah poses on their northern border and that the group must be pushed back so that the 60,000 Israelis who have fled their homes in the country’s north can return.

Hezbollah, which the United States considers a terrorist organization, says it will keep fighting until Israel’s attacks in Gaza cease and that it must defend Lebanon from Israeli aggression. Hundreds of thousands of Lebanese have fled their homes, including many from southern villages that Israel has largely destroyed.

Many Lebanese resent Hezbollah, whose military activities are outside of the state and not subject to any oversight, for dragging the country into a new war for the sake of Hamas.

But with Lebanon’s other political parties in disarray and the country’s economy suffering from a profound collapse, there are few other forces they can turn to for protection and to guide the country out of the spreading war.

His attitude has hardened in recent weeks, U.S. officials say, and American negotiators now believe that Hamas has no intention of reaching a deal with Israel.

Prime Minister Benjamin Netanyahu of Israel has also rejected proposals in the negotiations and added positions that have complicated the talks. U.S. officials assess that he is mainly concerned about his political survival and might not think a cease-fire in Gaza is in his interests.

Hamas has shown no desire at all to engage in talks in recent weeks, U.S. officials say. They suspect that Mr. Sinwar has grown more resigned as Israeli forces pursue him and talk about closing in on him.

A larger war that puts pressure on Israel and its military would, in Mr. Sinwar’s assessment, force them to scale back operations in Gaza, the U.S. officials said.

The war in the region has widened, but not in ways that have meaningfully benefited Hamas, at least not yet.

Immediately after Oct. 7, Hezbollah began carrying out strikes in northern Israel in a show of solidarity with Hamas. While the attacks drove Israelis from their homes, they did not put pressure on the military. Hezbollah’s leaders did not want to start a new war with Israel, U.S. officials assessed at the time.

Since the Israeli campaign against Hezbollah began last month, the group has not launched a major counterattack on Israel, much less opened an offensive front. Israeli and U.S. officials say Israel has destroyed half of the militia’s arsenal and killed many of its leaders.

Israeli troops moved into southern Lebanon this week, after a nearly monthlong bombing and sabotage campaign that included a strike that killed Hassan Nasrallah, the leader of Hezbollah.

Iran, which backs Hezbollah and Hamas, unleashed a missile barrage against Israel on Tuesday in response to the killing of Mr. Nasrallah. But most of the missiles were shot down or failed to do any real damage.

The failure of Hezbollah or Iran to meaningfully damage Israel, at least so far, is a telling sign of Mr. Sinwar’s miscalculation, American officials said.

Isolated and in hiding in Gaza, Mr. Sinwar’s communication with his organization has become strained. He stopped using electronic devices long ago and stays in touch with his organization through a network of human couriers, according to Israeli and American officials.

The pace of Israeli operations in Gaza has slowed, as Israeli leaders have shifted their attention to the north. Israeli forces are now in just a few positions in Gaza, including what they call the Philadelphi Corridor between the enclave and Egypt. While Israel has not launched a major raid into civilian areas of Gaza for weeks, it still conducts daily airstrikes targeting Hamas.

As a result, the toll on civilians in Gaza continues. In a 24-hour stretch on Wednesday and Thursday, the Israeli military killed 99 Palestinians in the enclave, local health officials said, one of the highest death tolls in months.

Talks to broker a cease-fire in Gaza and release the Israeli hostages have broken down. Mr. Netanyahu has added demands and revived some that had previously been dropped, frustrating international negotiators. And Mr. Sinwar has become far more inflexible, U.S. officials say.

His actions and motivations have long been a focus of the American intelligence community. But after Oct. 7, the spy agencies intensified their work on the Hamas leader, forming a targeting cell to study and hunt him.

For months, intelligence agencies have assessed that Mr. Sinwar has a fatalistic attitude and cares more about inflicting pain on Israelis than helping Palestinians. U.S. officials will not discuss their recent intelligence collection on him, but the view that his attitude is hardening comes from officials studying his negotiating stances and classified reports.

Mr. Sinwar’s position stiffened this summer after Israel assassinated Ismail Haniyeh, the political leader of Hamas based in Qatar and one of the chief negotiators. Mr. Haniyeh was a more conciliatory negotiator who was interested in making a deal, and U.S. officials say he was willing to push back against Mr. Sinwar’s more extreme demands. Israel’s decision to kill a top Hamas leader who was negotiating a cease-fire infuriated the group and Mr. Sinwar, according to U.S. officials.

Some Israeli officials have questioned whether Mr. Sinwar is still alive. U.S. and Israeli officials acknowledge there is no definitive proof of life. There have been no audio or video recordings from him for months.

On Sept. 13, Hezbollah released a letter that Mr. Sinwar sent in support of Mr. Nasrallah. Some Hamas officials, speaking elliptically, suggested that it was written outside Gaza by someone else, with Mr. Sinwar’s approval. It was not handwritten, unlike other communications that have been verified to come directly from him.

But American officials said they had no evidence he was dead, and in fact senior U.S. officials said they thought he was alive and making critical decisions for Hamas.

Mr. Sinwar remains in hiding but appears to recognize that Israeli forces are closing in on him. They came near his position in August, with Defense Minister Yoav Gallant of Israel saying that their forces had discovered signs that the Hamas leader had spent time in the warren of tunnels beneath Rafah, in southern Gaza.

“When we entered the tunnels under Rafah, where the hostages were murdered, we found signs of Sinwar’s past presence in Tel Sultan,” Mr. Gallant told reporters recently, referring to six hostages who were believed to have been killed in a neighborhood of Gaza, near Rafah.

While Mr. Sinwar’s strategy is not yet working, it could ultimately succeed.

Israeli forces are fighting Hezbollah on its home territory in southern Lebanon. While the Israeli government is promising a limited incursion in Lebanon, so far the military operations have been large-scale.

The fighting has already proved difficult: At least nine soldiers were killed in the first days of close-quarter combat. If the intense fighting continues, and Iran is drawn in, Mr. Sinwar could get his wish of a multifront war that eases pressure on Hamas.

Iran and Israel could continue to trade ballistic missile strikes. If one weapon causes immense damage, a larger conflict might erupt.

American officials are waiting to see whether the conflict between Iran and Israel escalates further. They do not believe that Iran wants a full-scale war with Israel or to directly intervene to help Hamas. But they also publicly support a planned Israeli strike against Iran in retaliation for the ballistic missile attack this week.

“Iran will hold a grudge for Nasrallah’s killing,” said Scott D. Berrier, a retired lieutenant general and the former head of the U.S. Defense Intelligence Agency. “But their options are limited. I don’t see Iran going toe to toe with Israel anytime soon.”

A senior U.S. official said Iran’s actions over the past few months had sent a clear message to Mr. Sinwar: “The cavalry is not coming.”

Julian E. Barnes and Adam Goldman reported from Washington, and Edward Wong reported from New York and Washington. Adam Rasgon and Aaron Boxerman contributed reporting from Jerusalem, and Ronen Bergman from Tel Aviv.

The strike set off huge explosions and left a ruined landscape of jagged concrete, twisted metal and smoldering debris in the Dahiya, a densely populated area where an Israeli strike on Sept. 28 killed Hezbollah’s longtime leader, Hassan Nasrallah.

Above is a look at who has been killed and targeted among Hezbollah’s leadership.