The news came on the eve of the war’s six-month anniversary on Sunday, when thousands are expected to gather in Israel for more protests.

“For six months we have been in a nightmare,” said Esther Buchstab, the mother of Yagev Buchstab, 34, who was taken from Kibbutz Nirim on Oct. 7, speaking at a vigil in Tel Aviv on Saturday evening in Israel. She added, “We demand that the state do everything to reach a deal, to bring back the living for rehabilitation and the murdered for burial.”

Nearby, in Democracy Square, thousands of antigovernment protesters called on Prime Minister Benjamin Netanyahu to bring home the more than 130 hostages still missing after Oct. 7.

As the protest was wrapping up, a car drove through the crowd of demonstrators in violation of police orders, wounding several people, according to a statement from police on Telegram. It wasn’t clear why the driver drove the car into the crowd, but the driver ignored police orders to stop and passengers in the car could be seen yelling at protesters in video posted on social media.

“‘Destroying Hamas’ and ‘absolute victory’ are meaningless slogans,” Eran Herkevi, 66, an agricultural specialist, said. “There is real pressure to bring back the remaining hostages, otherwise the public will never be able to recover as a society.”

These sentiments were echoed by Sarit Perl, 65, a retiree and the mother of three combat soldiers who are all in their second round of deployments. She called for Mr. Netanyahu to be impeached and for new elections to replace him.

“I’m here today, because there are three things that need to happen now: impeachment, bringing back all the hostages and holding elections,” she said.

Ms. Perl criticized Mr. Netanyahu, who is facing mounting calls for elections and whose home in Jerusalem has been the site of frequent protests, including earlier this week.

“Netanyahu has never functioned as a prime minister,” Ms. Perl said. “But now he appears to be acting to deliberately destroy the chances to succeed in reaching a deal, and nothing in Israel will ever recover as long as he remains in his position.”

Sahar Shapira, 42, said that the death of the hostage, Mr. Katzir, highlighted the urgent need for an agreement to return the hostages. “It is clear to people that the hostages cannot survive,” she said, predicting that “many others like him will return in a similar way.”

In an interview with The New York Times in 2009, after Palestinian rocket attacks led to a deadly three-week Israeli offensive against Hamas in Gaza, Mr. Katzir told a reporter that he had a nagging feeling. “I do not feel any victory,” Mr. Katzir said at the time, when the fighting had ended with a shaky cease-fire. “I still do not feel safe.”

News of Mr. Katzir’s death has inflamed tensions in Israel. In a statement announcing the vigil on Saturday, representatives of the relatives of hostages called on Israelis to gather in Jerusalem on Sunday for a rally marking six months of war.

Families of the abductees have organized rallies in a public plaza near the Israeli military headquarters in Tel Aviv every Saturday to pressure the government to make a deal for their relatives’ return. The gatherings have often converged with antigovernment protests.

Israeli officials are meeting with representatives from Egypt, Qatar and the United States in Cairo on Sunday to pick up discussions on a hostage deal that have been stalled for months. President Biden is pressuring participants to reach an agreement that leads to an “immediate cease-fire” and the return of hostages.

Noam Peri, the daughter of Chaim Peri, 79, who was taken from Kibbutz Nir Oz and who Hamas claimed in December was among five hostages killed in Gaza in an Israeli airstrike, demanded action from the Israeli government. “Mr. Prime Minister, members of the cabinet, this is on you!” she said, adding, “Do not come back without a deal!”

Mr. Katzir had lived in Nir Oz, a kibbutz near the border with the Gaza Strip. Over a quarter of its more than 400 residents were either killed or abducted in the attack — including Mr. Katzir’s father, Avraham, who was killed, and mother, Hanna, who was also taken hostage, according to the Israeli military.

Hanna Katzir was released in November as part of a brief cease-fire deal between Israel and Hamas in which more than 100 hostages were returned. The return of Ms. Katzir, 76, stunned some of her family members because Palestinian Islamic Jihad, a militant group backed by Iran, had earlier claimed that she was dead.

The families of the more than 130 hostages held in Gaza have expressed mounting anger and despair, saying that the Israeli government is not doing enough to reach a deal for their release. On Saturday, Mr. Katzir’s sister, Carmit Katzir, denounced the Israeli government for not reaching an agreement in time to secure her brother’s release.

“He could have been saved if there had been a deal in time,” she wrote of her brother on Facebook. “But our leadership are cowards, motivated by political considerations, and thus it did not happen.”

About 100 hostages are still being held by Palestinian militants in Gaza, according to the Israeli authorities; over 30 others are now presumed dead.

The Israeli military said that Mr. Katzir’s body had been recovered by troops in Khan Younis, a city in the southern part of Gaza where the Israeli army has been operating since December. Around 8 p.m. on Friday night, Israeli forces arrived in southern Khan Younis, isolated the area and excavated his body from where he was buried underground, the military official said.

Forensic pathologists in Israel confirmed his identity, and officials then informed his family, the military said. Mr. Hagari, the Israeli military spokesman, told reporters that he had spoken with Mr. Katzir’s sister after she posted her message on Facebook and expressed his condolences and an understanding of the urgency of the hostage situation.

Islamic Jihad had released at least two videos of Mr. Katzir, a farmer who was born in Nir Oz. He was last seen in a video released in early January, in which he said he had been held for more than 90 days and described hearing on the radio of the death of a close friend from Nir Oz.

Poland’s Ministry of Foreign Affairs noted on social media that Mr. Katzir was also a Polish citizen and conveyed its “deepest condolences” to family and friends. “May he rest in peace,” the post stated.

Over the past several weeks, Israel and Hamas have resumed indirect negotiations over a possible cease-fire and the release of at least some hostages. Hamas said in a statement on Telegram on Saturday that a delegation of its leadership would travel to Cairo on Sunday for further negotiations.

On Friday, President Biden sent messages to the leaders of Egypt and Qatar — who act as intermediaries between Hamas and Israel — urging them to increase pressure on Hamas to make a deal. He has pressed Israel’s prime minister, Benjamin Netanyahu, to do the same.

Israeli leaders have insisted that continued “military pressure” on Hamas will force the group to come to the table. The families of many of the hostages, fearing that their loved ones could be killed by their captors or by errant Israeli fire, have demanded more immediate action.

“Your story shouldn’t have ended like this,” Ms. Katzir wrote of her brother on Facebook on Saturday. “I’m sorry we couldn’t save you,” she wrote, adding, “I love you forever.”

Ephrat Livni contributed reporting.

Almost immediately, Iran’s leaders pledged that the strike would not go unpunished, a threat that was reiterated at funerals for several of the commanders and officers on Friday and Saturday in Iran, where large crowds of mourners and senior military officials gathered.

The Islamic Revolutionary Guards Corps, responsible for the security of Iran’s borders, called an attack against Israel “a national demand” in a statement issued Saturday. And Brig. Gen. Mohammad Bagheri, the commander in chief of Iran’s armed forces, said Saturday that Iran would “determine the time, place and method of the operation.” He added that the attack would be designed to inflict “maximum damage on the enemy to make it regret its action.”

American officials in Washington and the Middle East said on Friday that they were bracing for possible Iranian retaliation. On Thursday, Israel’s defense minister, Yoav Gallant, held a “multi-front situational assessment” in tandem with Israel’s security chiefs, according to his office.

Analysts have cautioned that while both sides probably want to avoid full-blown war involving Iran, any miscalculation could spill over and lead to a broader escalation. Israel has been trading fire with Iran-backed militant groups for months, particularly the Lebanese armed group Hezbollah, since the Hamas-led attack on Oct. 7 ignited the devastating war in Gaza.

Israel and Iran have been locked in a longstanding shadow war. Just this past December, Iran accused Israel of killing a high-level military figure, Brig. Gen. Sayyed Razi Mousavi, in a missile strike outside Damascus. A senior adviser to the Revolutionary Guards, General Mousavi was believed to have helped oversee the shipment of arms to Hezbollah. Israel, adopting its customary stance, declined to comment directly on whether it was behind the attack.

The Israeli military said this past week that it had scrambled GPS signals “in order to neutralize threats,” without elaborating. The jamming threw a wrench into commuters’ trips across central Israel, telling some users that they were in neighboring Lebanon.

Israeli combat soldiers expecting leave over the weekend have been ordered to remain deployed, the Israeli military said. And additional reserve units were called up to reinforce Israel’s air defense system.

“We have raised the readiness of combat units as needed, wherever it was necessary; we have reinforced our defense systems; and we have planes ready for defense and prepared to act in a variety of scenarios,” the Israeli military’s chief spokesman, Daniel Hagari, said on Thursday.

The investigation said that the workers had coordinated their mission in advance with the Israeli military and there is no suggestion that they had breached protocols established in Gaza. The humanitarian community has a longstanding practice in most parts of the world of avoiding nighttime travel when possible because, after dark, the risks that threaten their staff during the day are heightened. Karyn Beattie, team leader in Gaza for Save the Children, said that her organization avoided travel at night given the heightened risks and standard aid agency policies.

However, aid groups say that, in coordination with Israeli authorities, they have begun traveling at night, in part to avoid desperate crowds and get aid to centers where it can be distributed more widely.

Denise Habash Hazboun, a senior official at the relief organization Anera, said most aid groups have preferred on occasion to deliver food after midnight because “people won’t be on the roads.” Sandra Rasheed, Anera’s country director, said that between midnight and 3 a.m. was the “optimal time.”

It was unclear whether food deliveries had continued at night since Monday’s deadly airstrikes.

Organizations that deliver food, including the World Food Program and the main U.N. agency that aids Palestinians, UNRWA, have operated at night in recent months. They always get permission from the Israeli authorities and give soldiers information about their location and travel plans.

Israel, too, has sent at least one convoy of food to northern Gaza at night.

In February, Israeli forces opened fire at night as a crowd gathered near a convoy of aid trucks in Gaza City. Scores were killed and injured, according to Gazan officials and the Israeli military, which attributed most of the deaths to a stampede.

Officials from both sides offered differing accounts, but the deaths in a part of Gaza where starvation is rampant reflected desperation and lawlessness.

The Gazan Health Ministry said in a statement that Israeli forces had killed more than 100 people and had injured 700 others in a “massacre,” as they waited for food from the convoy.

An Israeli military spokesman, Rear Adm. Daniel Hagari, said that Israeli soldiers fired warning shots in the air before firing “only in face of danger when the mob moved in a manner which endangered them.”