DEIR AL-BALAH, Gaza Strip — An Israeli airstrike hit a school-turned-shelter in Gaza early Saturday, killing at least 80 people and wounding nearly 50 others, Palestinian health authorities said, in one of the deadliest attacks in the 10-month-old war between Israel and Hamas. A witness said it struck during prayers at a mosque in the building.

It was the latest in what the U.N. human rights office called “systematic attacks on schools” by Israel, with at least 21 since July 4, leaving hundreds dead, including women and children.

“For many, schools are the last resort to find some shelter and possible access to food and water,” it said shortly after Saturday’s attack.

Hamas Command Center in School: Israel

The Israeli military acknowledged it targeted the Tabeen school in central Gaza City, saying it hit a Hamas command center in the school. Hamas denied that.

Video from the scene showed walls blown out on the ground level of a large building. Concrete chunks and twisted metal lay on the blood-soaked floor, along with clothing, furniture and other debris. Bodies, some in bloodstained shrouds, were placed shoulder to shoulder in makeshift graves, making room for more.

Fadel Naeem, director of the al-Ahli hospital in Gaza City, told The Associated Press that the facility received 70 bodies along with the body parts of at least 10 others. Gaza’s Health Ministry said another 47 people were wounded.

Naeem said some of the wounded had severe burns and many had limbs amputated.

“We received some of the most serious injuries we encountered during the war,” he said.

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Strike Comes Before Sunrise as People Prayed

The strike hit without warning before sunrise as people prayed at a mosque inside the school, according to Abu Anas, a witness who worked to rescue people.

“There were people praying, there were people washing and there were people upstairs sleeping, including children, women and old people,” he said, prayer beads in his hand. “The missile fell on them without warning. The first missile, and the second. We recovered them as body parts.”

Three missiles ripped through the two-story building — the first floor housing the mosque and the second the school — where about 6,000 displaced people were taking shelter from the war, said Mahmoud Bassal, a spokesperson for the Civil Defense first responders, who operate under the Hamas-run local government.

Many of the dead were unrecognizable, and many of the casualties were women and children, he said.

The U.N. previously said that as of July 6, 477 out of 564 schools in Gaza had been directly hit or damaged in the war, adding that Israel has a duty under international law to provide safe shelter for the displaced.

“There’s no justification for these massacres,” European Union foreign policy chief Josep Borrell said in a statement posted on X, in reference to strikes on schools. U.K. Foreign Minister David Lammy said that he was “appalled.”

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Israeli intelligence indicated that about 20 militants from Hamas and Islamic Jihad, including senior commanders, were using the Tabeen school compound to plan attacks on Israeli forces, Lt. Col. Nadav Shoshani, an Israeli military spokesman, said in a statement on X. Shoshani also questioned the casualty numbers issued by the Health Ministry.

Izzat al-Rishq, a top Hamas official, denied that there were militants in the school.

Israel has blamed civilian deaths in Gaza on Hamas, saying the group endangers noncombatants by using schools and residential neighborhoods as bases for operations. The U.N. human rights office acknowledged that colocating combatants with civilians is a violation of international humanitarian law, but that Israel must also comply with the law’s principles of precaution and proportionality.

Israel also said the school was located next to a mosque serving as a shelter.

A camera operator working for the AP said, however, that the mosque and classrooms were in one building, with the prayer hall on the ground floor and the school above it. A missile appeared to have penetrated the floor of the classrooms to the mosque below and exploded, according to the camera operator.

Renewed Push for Cease-Fire

The strike came as U.S., Qatari and Egyptian mediators renewed their push for Israel and Hamas to achieve a cease-fire agreement that could help calm soaring tensions in the region following the assassination of Hamas political leader Ismail Haniyeh in Tehran and a senior Hezbollah commander in Beirut.

Egypt, which borders Gaza, said that the strike on the school showed that Israel had no intention of reaching a cease-fire deal and ending the war. Neighboring Jordan condemned the attack as a “blatant violation” of international law. Qatar demanded an international investigation, calling it a “heinous crime” against civilians.

Late Friday, two separate airstrikes in central Gaza killed at least 13 people, including three children and seven women, hospital authorities said. An AP journalist counted the bodies at the al-Aqsa Martyrs hospital in the central city of Deir al-Balah.

One strike hit a house in the Nuseirat refugee camp, killing seven people, all but one of them women, hospital officials said. Another hit a house in Deir al-Balah, killing six, including a woman and her three children, the hospital said.

Israel’s campaign in Gaza has killed more than 39,790 Palestinians and wounded more than 92,000 others, according to the Health Ministry, which doesn’t distinguish between combatants and civilians in its tally. The war was triggered by Hamas’ Oct. 7 attack in which militants from Gaza stormed into southern Israel, killing around 1,200 people and abducting 250 others.