Gaza’s health ministry says that Israel is striking medical facilities.

Israel has said its strikes are targeting all sites connected with Hamas, the armed Palestinian group that controls the Gaza Strip, including the homes of members. Israel said it believes Hamas members are hiding in homes, schools and hospitals. Because its members are Palestinians from Gaza, they live among the community.

Seven hospitals have been struck with Israeli airstrikes and one of them was bombed out of operation, Mr. al-Qidra said. His account could not be immediately verified, but the United Nations has said that at least two hospitals, multiple homes and two centers run by the Palestine Red Crescent Society have been hit.

The strikes came as part of Israel’s response to Saturday’s attack, when hundreds of Palestinian gunmen swept across Israel’s border with Gaza, killing hundreds of civilians and soldiers and firing thousands of rockets toward the center of the country. On Monday, Israel’s defense minister announced a “complete siege” of Gaza, saying “no electricity, no food, no water, no fuel” would be allowed in.

Volker Türk, the United Nations’ high commissioner for human rights, on Tuesday warned that a full siege of Gaza would exacerbate the “already dire” humanitarian situation in the coastal territory and would hurt hospitals’ ability to treat the growing number of wounded.

At least 765 Palestinians have been killed since Saturday and 4,000 injured, according to Gaza’s health ministry.

Gaza, a small densely populated enclave that is home to more than two million people, has been under a severe blockade imposed by Israel, and backed by Egypt, for 16 years, limiting what can go in, including medicines and medical equipment.

“The hospitals in Gaza are in a very critical situation as a result of this oppressive siege and has led to a big shortage of medicine and medical tools and fuel,” Mr. al-Qidra said, referring to the new bombardment. “Everyone needs to bear responsibility to save the medical work in Gaza.”

The heavy Israeli bombardment has made movement in the streets dangerous and ambulances have had difficulty transporting the dead and wounded. Instead, people have at times relied on borrowed vehicles, tuk-tuks or motorcycles.

The health ministry said that at least nine ambulances had been struck since Saturday.

“The health system was already suffering before this war,” said Dr. Mohammed Abu Mughaiseeb, the deputy medical coordinator in Gaza for Doctors Without Borders, widely known by its French name, Médecins Sans Frontières.

He said he has seen people coming to schools and hospitals for shelter because they feel these are the safest areas — though they may not be. A building next to Al-Shifa hospital, Gaza’s largest, was struck, he said, and shrapnel hit the hospital.

“If the current situation continues, we are now in day four, there will be a critical impact not just on the medical system but on every aspect of life in Gaza,” he said.

Prime Minister Fumio Kishida said Sunday on X, the social media platform formerly known as Twitter, that Japan “strongly condemns the attacks which severely harmed innocent civilians” but added that “Japan is deeply concerned about a number of casualties in Gaza as well” and urged “all the parties” to “exercise maximum restraint.”

After a telephone call with Ayman Safadi, Jordan’s foreign minister, Yoko Kamikawa, Japan’s newly appointed foreign minister, issued a statement on Monday condemning the attacks and kidnappings by Palestinian gunmen, but added that “Japan is deeply concerned about a number of casualties caused by the attacks by the Israeli side.”

During a news conference on Tuesday in Tokyo, a reporter asked Hirokazu Matsuno, the chief cabinet secretary, why Japan had not signed the joint statement from the White House and its European allies, which condemned Hamas and described the allies as “common friends of Israel.”

Mr. Matsuno offered a technical answer, saying that “the international community has traditionally expressed its position on Middle East issues within various frameworks, and I understand that the statement you pointed out was issued within one of those frameworks.”

He added that Japan would “cooperate with the international community, including the G7, and strengthen its efforts to reach out to both Israel and Palestine, and will make every effort to calm the situation.”

Japan’s effort to balance its response may reflect a desire not to conflate Hamas, a militant group, with Palestinian civilians. Some European leaders have also said that there should be a distinction between Hamas and Palestinians.

Hikari Hida contributed reporting.

In an interview on Wednesday, Ali Barakeh, a Beirut-based foreign relations official with Hamas, said that 2,000 of the group’s fighters had participated in the initial attack on Israel on Saturday morning. Fighters from other armed Palestinian factions joined once the operation was underway, he said.

Hamas, which is supported financially and militarily by Iran, became notorious during the second Palestinian uprising that began in 2000 by dispatching large numbers of suicide bombers to civilian areas in Israel. In more recent years, it has developed a large arsenal of rockets that it regularly fires from Gaza at communities in Israel.

Its fighters in Gaza carry assault and sniper rifles, rocket-propelled grenades and other arms and are believed to move around the territory via tunnels that conceal their movements from Israeli drones. Analysts say those capabilities could enable them to fight a prolonged guerrilla war if Israel, which has pledged to destroy Hamas militarily, launches a ground invasion of Gaza.

From the homes lining a terrace, Israeli soldiers on Tuesday morning carried stretchers bearing the bodies of three residents slain by Palestinian fighters, and placed them on the back of a truck. An untold number remained inside, the soldiers said.

Several homes were burned out. Inside, bullet holes riddled some of the ceilings. An unexploded grenade lay under a kitchen table.

This was the scene of some of the worst bloodshed on Saturday, after gunmen surged across the border from Gaza, a mile and a half to the west, gunning down an unknown number of the village’s 750 residents. A New York Times photographer and I were among the first journalists allowed into the village since the deadly assault.

“It’s not a war or a battlefield, it’s a massacre,” said Maj. Gen. Itai Veruv, an Israeli officer on the scene. “It’s something I never saw in my life, something more like a pogrom from our grandparents’ time.”

There were more than a dozen bloated bodies lying on the ground, some of them Israelis. But some were dead Palestinian fighters — killed during a gun battle when Israeli soldiers finally retook control of the village. Nearby were the remains of a wrecked pickup truck and a hang-glider, two of the vehicles used by the gunmen to cross the border into Israel.

A dead man’s legs poked out from underneath a bush.

Traveling to Kfar Azza on Tuesday, we drove through several similar scenes, and saw dozens of shot-up and burned-out cars. Rows of tanks, armored vehicles and Israeli soldiers secured the road. But while we were in the village, frequent rocket fire from Gaza sent us rushing for cover.

In between the booms, we were left with the eerie sound of silence.

But he added: “Those who say that the recent saga is the work of non-Palestinians have miscalculated.”

The comments were the Iranian government’s latest denial of involvement in the incursion. On Monday, Nasser Kanaani, a spokesman for Iran’s Foreign Ministry, said that efforts to blame Tehran for the attack were a “political attempt to justify support for Israel.”

Israeli officials have said publicly that they have not determined whether Iran, which provides funding to Palestinian militant groups including Hamas, which controls Gaza, was behind the attack. And the White House said on Monday that it still had no evidence that Tehran was directly involved in planning or executing the attack.

Iran, which does not recognize the state of Israel, has positioned itself as a key supporter of the Palestinian cause, and Mr. Khamenei delivered his speech wearing a Palestinian scarf. He repeatedly referred to Israel as “the Zionist regime,” a term favored by Iran’s ruling clerics, and warned that it would face consequences if it continued to conduct deadly strikes against Palestinians.

“The heads and decision makers of the usurping Zionist regime and its supporters should know that the massacre and mass killing of the people of Gaza will bring a greater calamity on them,” he said.

As Israeli warplanes struck hundreds of sites on Monday, Israel’s defense minister said that “no electricity, no food, no water, no fuel” would be allowed into Gaza, which is controlled by the militant group Hamas and is under a 16-year blockade by Israel and Egypt that heavily restricts access for people and goods. Mr. Türk said in a statement that the ability of medical facilities to treat the growing number of people wounded in Israeli strikes would be harmed by a “full siege.”

“The imposition of sieges that endanger the lives of civilians by depriving them of goods essential for their survival is prohibited under international humanitarian law,” Mr. Türk said. He added that restrictions on people and goods must be “justified by military necessity” or may amount to collective punishment.

The Palestinian Health Ministry in Gaza warned on Sunday of large shortages of medicine and health equipment, as well as fuel required to keep hospital electrical generators running.

Mr. Türk also said he was “deeply shocked and appalled by allegations of summary executions of civilians, and, in some instances, horrifying mass killings by members of Palestinian armed groups.” He called on Palestinian armed factions to immediately release Israeli civilians who were taken hostage. About 150 people are believed to have been abducted by Palestinian gunmen in the attacks that began on Saturday.

“It is horrific and deeply distressing to see images of those captured by Palestinian armed groups being ill-treated, as well as reports of killings and the desecration of their bodies,” he said. “Civilians must never be used as bargaining chips.”

Peter Stano, the spokesman for the European Commission, said that taking civilians hostage is “appalling” and “against any law and any norm of civilized behavior.” He added: “Israel has the right to defend itself and its citizens.”

Officials who planned to grapple with the lingering economic effects of the coronavirus pandemic and Russia’s war in Ukraine now face a new crisis.

“Economies are at a delicate state,” Ajay Banga, the World Bank president, said in an interview on the sidelines of the annual meetings. “Having war is really not helpful for central banks who are finally trying to find their way to a soft landing,” he said. Mr. Banga was referring to efforts by policymakers in the West to try to cool rapid inflation without triggering a recession.

Mr. Banga said that so far, the effect of the Middle East attacks on the world’s economy is more limited than the war in Ukraine. That conflict initially sent oil and food prices soaring, roiling global markets given Russia’s role as a top energy producer and Ukraine’s status as a major exporter of grain and fertilizer.

“But if this were to spread in any way, then it becomes dangerous,” Mr. Banga added, saying such a development would result in “a crisis of unimaginable proportion.”

Colonel Hecht said that Israel would strike Gaza, the impoverished coastal territory over which it exercises a blockade, with extraordinary severity because of the level of harm that fighters had wrought during their assault on southern Israel.

“The dynamic right now in Gaza is that the scope of this is going to be bigger than before and more severe,” Colonel Hecht said.

“We should all change the paradigm here,” he added. “It’s not the regular, small, contained Gaza tit-for-tat.”

He also said that the Israeli Air Force was too stretched to fire the warning strikes — known as “roof knocks” — that it has fired in previous Gaza conflicts to encourage Palestinian civilians to leave an area before it is hit with larger missiles.

“Because we have right now this very, very big-scale event,” Colonel Hecht said, “we are stretched with our aerial assets, we’re stretched with our munitions.” It was not possible to verify his claim.

He declined to say whether the air force’s strikes would be affected by the presence inside Gaza of around 150 Israeli hostages who are believed to be held there by Palestinian fighters since being abducted on Saturday.

Colonel Hecht also said that at least one Israeli officer had been killed on Monday on Israel’s northern border with Lebanon, after four fighters from Lebanon tried to cross it.

She served for many years on the board of directors of B’Tselem, an Israeli human rights organization that said Israel was an apartheid state. She made visits to the occupied territories to express solidarity with Palestinians and volunteered with an organization that drove sick Palestinians from Gaza into Israel for medical treatment. She is the executive director of the Negev Institute for Strategies of Peace and Development and co-founded the Arab Jewish Center for Equality Empowerment and Cooperation.

One of her sons, Yonatan Zeigen, told the Israeli newspaper Ha’aretz that he last communicated with her on Saturday morning, when she said she was hiding in a closet in a safe room on the kibbutz. They started to text rather than speak as the sound of shooting got closer, but there was no communication from her after 11:07 a.m., he said.

Ms. Silver is “probably worried sick about the Palestinian contacts in her phone, a friend wrote on Facebook. “She probably thinks of the danger they will now face for being seen as collaborators with the enemy.”

That peace-oriented Israelis were among Hamas’s targets has fueled further resentment of the Netanyahu government, which was caught by surprise on Saturday when Hamas fighters from the Gaza Strip streamed into Israel on Saturday, meeting little resistance.

Some Israelis said that, by contrast, the country’s military forces had been beefed up to protect settlers in the West Bank, who have clashed repeatedly with Palestinian residents.

Rachel Gur, an Israeli involved in the search for the missing, said that many of the residents of the collectives near Gaza had similar politics. “These are kibbutzniks, the people who vote for the left, who support coexistence,” she said. “You’re talking about the old time secular leftists, who want peace, who are against annexation.”

Another peace activist, Hayim Katsman, was initially believed to have been taken hostage on Saturday but was found killed in his home on Kibbutz Holit, near the southern end of Gaza. He had studied conservative trends and radicalism within the Zionist religious community, and played bass guitar and worked as a D.J. playing Arabic music.

He did gardening and landscaping at Kibbutz Holit, his mother, Hannah Wacholder Katsman, said. He had also worked as a mechanic, and taught at various colleges and pre-army programs. On her Facebook page, she mourned him as “beautiful, generous and talented.” He was also “very industrious and independent,” she said in a text message on Monday.

Mr. Katsman recently completed his doctorate at the University of Washington in Seattle, where he won an award for the best graduate paper in the Association for Israel Studies. During his time there, he served as co-coordinator of the Israel-Palestine research group at the university.

His doctorate was titled, “Religious nationalism in Israel/Palestine.” It is unusual for Israelis to refer to the region in that way, rather than simply as “Israel,” or “Israel and the occupied territories.”

Bilha and Yakovi Inon, who were peace activists and the parents of a prominent activist, Maoz Inon, were also killed on Saturday. The couple were killed in their farming collective, of Netiv Ha’Asara, which lies just north of Gaza.

“You see a lot of broken spirits wandering around right now,” said Jonathan Celestino, 26, an employee of the Bernard Horwich Jewish Community Center in Chicago, “because so many people are hurt, scared and concerned.”

The small but diverse Jewish community in America — numbering about 7.5 million in 2020, or 2.4 percent of the U.S. population — has long been polarized over how to address the Israeli-Palestinian conflict. In more recent months, American Jews have also been split over the far-right Israeli government’s push to limit judicial authority.

But many Jewish leaders said the targeted killing of hundreds of civilians by Hamas and the threats to kill kidnapped hostages had brought a sense, at least for now, of unity.

At Congregation Beth Elohim in Park Slope, Brooklyn, a Reform synagogue, Rabbi Rachel Timoner has long criticized the Israeli government and its occupation of Palestinian territories. Just weeks ago, she recalled in an interview on Monday, she delivered a Rosh Hashana sermon that described loyalty to Israel as “standing with Israelis against this government.” It drew a standing ovation, she said.

But an hour before she was set to deliver another sermon on Saturday morning, reports emerged of the attack by Hamas, the Palestinian faction that controls Gaza. She quickly understood, in the midst of her horror, what her message must be.

“Now is a time to stand unequivocally with Israel and Israelis,” she recalled telling her congregants, “and to say to our Israeli family that we are grieving with them, and we are praying now that Israel will defeat Hamas.”

Rabbi Motti Seligson, a spokesman for Chabad, a global network of strictly observant Jewish congregations, said he was celebrating the Jewish holiday of Simhat Torah in Brooklyn on Saturday with visitors from Israel — some of whom had to travel home and report for military duty after the attacks.

He said it was a time for Jews to “double down on being Jewish,” and pray and light candles for Israel.

Prayer was a response across the country, including at a vigil on Monday evening in Providence, R.I., where Stephanie Hague, chief policy officer at the Jewish Alliance of Greater Rhode Island, said it felt like one small way to show support for Israel.

“It feels like one of the only things we can do,” she said. “It feels like we’re so far away.”

In Los Angeles on Sunday night, a vigil drew some 2,000 people to the Stephen Wise Temple, where attendees gripped each other’s shoulders, hugged and swayed to music in the cavernous worship hall. There was applause when speakers reminded them to stay strong and support Israel, including monetarily.

A handful of attendees cloaked themselves in the Israeli flag as the evening drew to a close.

“The people here, they want to help,” said Miriam Zlotolow, 78, a retiree who immigrated to the United States from Israel when she was 21. “They want to draw strength from each other.”

For many Jews, the distress was heightened by connections to friends, relatives or colleagues in Israel, some still missing or unaccounted for on Monday.

Rabbi David Wolpe, a visiting scholar at Harvard Divinity School, described obsessively watching the news in recent days while keeping in constant contact with friends in Israel. “I know any number of people whose kids have been mobilized and who spent nights in safe houses, who’ve lost friends or have had friends kidnapped,” he said.

Like others, he said he feared what lay ahead, and the likelihood that the toll would grow. “As a human being, and as a rabbi, the last thing I want to see is innocents dying for the decisions of their leaders,” he said.

At Brandeis University in Waltham, Mass., a school founded by American Jews, the mood was solemn on Monday, said Ronald Liebowitz, the university’s president, who spent part of the day roaming the campus and talking to students. Many were grieving on behalf of a well-known emeritus professor, Ilan Troen, whose daughter and son-in-law were killed in the attack while protecting their 16-year-old son, who survived.

While he is preparing for the possibility of growing tension between campus groups that hold opposing views on the Israeli-Palestinian conflict, Mr. Liebowitz said he sensed the usual campus debates had been placed on hold.

“Politics, at least here, seem to be set aside for now,” he said, adding: “No one I know is looking at those issues of politics now. They’re looking at the savagery of these attacks.”

Anna Betts contributed reporting.

“This is not some distant tragedy,” Mr. Biden said in the statement. “The ties between Israel and the United States run deep. It is personal for so many American families who are feeling the pain of this attack as well as the scars inflicted through millennia of antisemitism and persecution of Jewish people.”

He noted that police departments across the United States had “stepped up security around centers of Jewish life, and the Department of Homeland Security, the Federal Bureau of Investigation, and other federal law enforcement partners are closely monitoring for any domestic threats” in connection with the attacks in Israel.

A number of Americans who had been visiting Israel during the attack, including two lawmakers — Senator Cory Booker of New Jersey and Representative Dan Goldman of New York — were able to leave the country over the weekend. Mr. Biden directed Americans trying to leave Israel to seek out remaining “commercial flights and ground options” and urged all American citizens in Israel to “please also take sensible precautions in the days ahead and follow the guidance of local authorities.”

Mr. Biden spoke with the Israeli prime minister, Benjamin Netanyahu, in a call on Sunday, in which they discussed the hostages taken by Hamas, as well as what military assistance the United States could provide. The Pentagon announced the same day that it was sending additional munitions to Israel and moving more Navy warships, including an aircraft carrier, and combat aircraft closer to Israel in a show of support. Secretary of State Antony J. Blinken said the United States was working to fulfill several specific requests from Israel for military assistance, without providing details.

On Monday, Defense Department officials said the Pentagon had offered the assistance of U.S. Special Operations forces for planning and surveillance in any hostage recovery efforts. A White House spokesman also clarified that the U.S. government was not sure that American were being held. “We can’t confirm that they are, in fact, holding hostages,” John F. Kirby, the spokesman, told reporters. There are, he said, Americans who are unaccounted for and may be captive.

In the statement on Monday, Mr. Biden evoked the Sept. 11, 2001, attacks on the United States, lamenting the deaths of more Americans in an extremist attack.

“We remember the pain of being attacked by terrorists at home, and Americans across the country stand united against these evil acts that have once more claimed innocent American lives,” Mr. Biden said. “It is an outrage.”

The White House will be lit up in the blue and white colors of the Israeli flag on Monday night to express solidarity with Israel. It will be the latest landmark around the world to be so illuminated, joining the Empire State Building in New York, the Brandenburg Gate in Berlin and the Sydney Opera House in Australia, among others.

Eric Schmitt and Peter Baker contributed reporting.

Video

In messages with The New York Times, family members of the woman identified her as Shiri Silverman Bibas, and her sons as Ariel, 4, and Kfir, 9 months.

Ms. Bibas’s husband, Yarden Bibas, and her parents, Yossi Silberman, 67, and Margit Silberman, 64, are also missing, according to Ms. Bibas’s sister, Dana Sitton. Ms. Silberman has Parkinson’s disease, Ms. Sitton said.

Mr. Al-Najjar, a freelance reporter who posted the footage to social media, initially entered Israel through a breach in the fence along the perimeter with Gaza. He said it was the first time he had ever left Gaza in his life, because of the blockade imposed by Israel and backed by Egypt that restricts movement in and out of the enclave.

In an interview, he provided a window into how some members of the large, loose-knit group of men he saw moving on Nir Oz seemed more organized, carrying weapons and wearing military-style gear. Others appeared to be tagging along as onlookers.

In the video below, he captured fleeting glimpses of men en route to Nir Oz riding in carts with guns, or walking unarmed in civilian clothes and sandals.

Video

When Mr. Al-Najjar arrived at Nir Oz, he appeared on camera describing a chaotic scene while what appeared to be gunfire rang out nearby.

Video

As Mr. Al-Najjar was filming the abductions, he said he tried to offer consolation.

“I wanted to tell a woman who was captured with children, ‘Be calm and patient,’” Al-Najjar told The New York Times. “But I realized I didn’t speak her language.”

Ms. Sitton, Ms. Bibas’s sister, expressed the wrenching pain of waiting to hear news about the fate of the family.

“I don’t know if Shiri has bottles, diapers and baby food for the baby, Kfir. I don’t know how she is feeding him,” Ms. Sitton said. “I can’t sleep, can’t eat just thinking about them. How do they treat them?”

Several other residents of Nir Oz were apparently kidnapped as well, including a man identified by residents as Gadi Mozes, who was photographed by Mr. Al-Najjar.

Mr. Al-Najjar said that as he was leaving Nir Oz, he saw at least two gunmen whose faces he recognized lying dead in a field, and he thought there were likely others.

“There are dozens missing there, as well as dead and injured,” Mr. Al-Najjar said. “No one knows how many.”

Additional production by Meg Felling.

Israel has been at war with Gaza since hundreds of Hamas gunmen surged across the border from Gaza on Saturday, overrunning Israeli border towns and villages, killing civilians in their homes, massacring partygoers at an open-air music festival and taking scores of people, young and old, back to Gaza as hostages.

More than 800 Israelis have been killed so far, according to officials, at least 85 of them soldiers.

Most Jewish 18-year-olds are drafted for compulsory military service in a country of 10 million people, and many continue to volunteer for reserve duty into middle age. That means that most families would have someone, or know someone, taking part in the war.

Yaacov Ben Yaacov, 57, a tech entrepreneur, knows many. His three sons, two nephews and a son-in-law are all in uniform now. The youngest son, 20, is performing his obligatory service and his older brothers, in their late 20s, have been called up for reserve duty. One son is a medic in a combat unit and two are in commando units.

One nephew, also in his late 20s, came back early on Monday from a trip to the United States to report for duty and was on his way down south, Mr. Ben Yaacov said.

“As they say, it hits close to home,” he said.

Still, he said it was good to have a country with an army that can protect its people “and not go into gas chambers,” referring to the Jews during the Holocaust.

“So with all the hardship and emotional stress, we have no alternative,” he said. “The alternative is to have more of what happened on Saturday. To tell you as a father or grandfather am I happy to see my kids in harm’s way? No, but we have no choice.”