DEIR AL-BALAH, Gaza Strip — An Israeli strike early Thursday on a school sheltering displaced Palestinians in central Gaza killed at least 33 people, including 12 women and children, according to local health officials. The Israeli military said that Hamas militants were operating from within the school.

It was the latest instance of mass casualties among Palestinians trying to find refuge as Israel expands its offensive. A day earlier, the military announced a new ground and air assault in central Gaza, pursuing Hamas militants it says have regrouped there.

Troops repeatedly have swept back into parts of the Gaza Strip they have previously invaded, underscoring the resilience of the militant group despite Israel’s nearly eight-month onslaught.

Witnesses and hospital officials said the predawn strike hit the al-Sardi School, run by the United Nations agency for Palestinian refugees known by the acronym UNRWA. The school was filled with Palestinians who had fled Israeli operations and bombardment in northern Gaza, they said.

The hospital initially reported that nine women and 14 children were among those killed in the strike on the school. The hospital morgue later amended those records to show that the dead included three women, nine children and 21 men. It was not immediately clear what caused the discrepancy. An Associated Press reporter had counted the bodies but was unable to look beneath the shrouds.

Separate strikes in central Gaza killed another 15 people, nearly all men.

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Witness Accounts and Military Statements

Ayman Rashed, a man displaced from Gaza City who was sheltering at the school, said the missiles hit classrooms on the second and third floor where families were sheltering. He said he helped carry out five dead, including an old man and two children, one with his head shattered open. “It was dark, with no electricity, and we struggled to get out the victims,” Rashed said.

Rear Adm. Daniel Hagari, the spokesman for the Israeli military, said it carried out a “precise strike” based on concrete intelligence that militants were planning and conducting attacks from inside three classrooms. He said only those rooms were attacked.

“We conducted the strike once our intelligence and surveillance indicated that there were no women or children inside the Hamas compound, inside those classrooms,” he said.

Hagari said there were around 30 suspected militants in the three rooms. He said the military had confirmed killing nine of them, and displayed a slide showing their names and photos. He provided no other evidence to substantiate the military’s claims.

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Overwhelmed Hospitals and Refugee Camps

Casualties from the strike arrived at the Al-Aqsa Martyrs Hospital in nearby Deir al-Balah, which had already been overwhelmed by a stream of constant ambulances since the central Gaza incursion began 24 hours earlier, said Omar al-Derawi, a photographer working for the hospital.

Videos circulating online appeared to show several wounded people being treated on the floor of the hospital, a common scene in Gaza’s overwhelmed medical wards. Electricity in much of the hospital is out because staff are rationing fuel supplies for the generator.

“You can’t walk in the hospital — there’s so many people. Women from the victims’ families are massed in the hallways, crying,” he said.

The school was in Nuseirat, one of several built-up refugee camps in Gaza dating to the 1948 war surrounding Israel’s creation, when hundreds of thousands of Palestinians fled or were driven from their homes in what became the new state.

Footage showed bodies wrapped in blankets or plastic bags being laid out in lines in the courtyard of the hospital. Mohammed al-Kareem, a displaced Palestinian sheltering near the hospital, said he saw people searching for their loved ones among bodies, and that one woman kept asking medical workers to open the wraps on the bodies to see if her son was inside.

“The situation is tragic,” he said.

Philippe Lazzarini, the commissioner-general of UNRWA, said in a post on X that 6,000 people were sheltering in the school when it was hit without prior warning. He said UNRWA was unable to verify claims that armed groups were inside.

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UNRWA schools across Gaza have functioned as shelters since the start of the war, which has driven most of the territory’s population of 2.3 million Palestinians from their homes.

Last week, Israeli strikes hit near an UNRWA facility in the southern city of Rafah, saying they were targeting Hamas militants. An inferno ripped through tents nearby housing displaced families, killing at least 45 people. The deaths triggered international outrage, and Israeli Prime Minister Benjamin Netanyahu said the fire was the result of a “tragic mishap.” The military said the fire may have been caused by secondary explosions. The cause of the explosions has not been determined.

Israel sent troops into Rafah in early May in what it said was a limited incursion, but those forces are now operating in central parts of the city. More than 1 million people have fled Rafah since the start of the operation, scattering across southern and central Gaza into new tent camps or crowding into schools and homes.

Israel launched its campaign in Gaza after Hamas’ Oct. 7 attack into Israel, in which militants killed some 1,200 people and took another 250 hostage. Israel’s offensive has killed at least 36,000 Palestinians, according to Gaza’s Health Ministry, which does not distinguish between fighters and civilians in its figures.

Israel blames civilian deaths on Hamas because it positions fighters, tunnels and rocket launchers in residential areas.

The United States has thrown its weight behind a phased cease-fire and hostage release outlined by President Joe Biden last week. But Israel says it won’t end the war without destroying Hamas, while the militant group is demanding a lasting cease-fire and the full withdrawal of Israeli forces.

Far-right members of Netanyahu’s government have threatened to bring down the coalition if he signs onto a cease-fire deal.

Israel has routinely launched airstrikes in all parts of Gaza since the start of the war and has carried out massive ground operations in the territory’s two largest cities, Gaza City and Khan Younis, that left much of them in ruins.

The military waged an offensive earlier this year for several weeks in Bureij and several other nearby refugee camps in central Gaza.

Troops pulled out of the Jabalia camp in northern Gaza last Friday after weeks of fighting caused widespread destruction. First responders have recovered the bodies of 360 people, mostly women and children, killed during the battles.