An Israeli airstrike on a Gaza City school compound housing displaced Palestinian families killed around 100 people, the Gaza Civil Emergency Service said on Saturday.
Israel said around 20 fighters had been operating at the compound.
Video from the site showed body parts scattered around and more bodies being carried away and covered in blankets on the floor. Empty food tins lay in a puddle of blood, and burnt mattresses and a child's doll lay among the debris.
In another video, men prayed over a dozen body bags laid out on the ground of the Tabeen school complex.
The territory's Civil Emergency Service, which has a credible track record in stating casualty numbers, and the Hamas-run government media office said in separate statements that the complex had been attacked as its occupants were performing dawn prayers.
"So far, there are more than 93 martyrs, including 11 children and six women. There are unidentified remains," Palestinian civil defense spokesperson Mahmoud Bassal told a televised press conference.
Tens of thousands of displaced Palestinians have sought shelter in Gaza's schools, most of which have been closed since the war began 10 months ago.
Around 350 families had been sheltering at the compound, Bassal said - some of the hundreds of thousands of Palestinians displaced from their homes by Israel's onslaught on Gaza.
The upper floor housing families and the lower floor, used as a mosque, were both hit, he said.
The Israeli military said the death toll was inflated.
"The compound, and the mosque that was struck within it, served as an active Hamas and Islamic Jihad military facility," Lieutenant Colonel Nadav Shoshani said on X.
He said the numbers published by the Hamas-run media office did not appear to correspond to the Israel Defense Forces' information, but the army provided no evidence of that.
An IDF official said the part of the mosque that was struck was reserved for men.
"This was verified by intelligence, and the strike was carried out using three small, precise munitions which cannot cause the scale of damage that the Palestinians are reporting," the official said.
It was not immediately clear which floor or floors the videos had been filmed on.
Israel says Palestinian fighters embed themselves among Gaza's civilians, operating from within schools, hospitals and designated humanitarian zones - which Hamas and its allies deny.
Hamas said the strike was a horrific crime and a serious escalation. Izzat El-Reshiq of Hamas' political office said the dead did not include a single combatant.
A separate strike on Saturday killed three Palestinians in Al-Nuseirat in central Gaza and another killed one person in nearby Deir Al-Balah, medics said.
NEW ROUND OF CEASEFIRE TALKS
The European Union's foreign policy chief Josep Borrell said on X that he was horrified by the images from the school.
A spokesperson for Palestinian President Mahmoud Abbas, Nabil Abu Rudeineh, urged Israel's ally Washington to put an end to "blind support that leads to the killing of thousands of innocent civilians, including children, women, and the elderly".
Egypt, Qatar, the United Arab Emirates, Saudi Arabia and Türkiye all condemned the strike.
Senior Hamas official Sami Abu Zuhri said it should serve as a turning point as mediators push to resume ceasefire talks.
A Hamas official told Reuters the group was studying a new proposal for discussion but did not elaborate.
Egypt said the killing of Gaza civilians showed Israel had no intention of ending the war. Qatar's foreign ministry described the strike as a "horrific massacre".
Speaking to Al-Jazeera television, Khalil Al-Hayya, the head of the Hamas team for the indirect ceasefire talks with Israel, said statements of condemnation were no longer sufficient.
"Dismiss (Israeli) ambassadors, close down embassies, and sever ties with the occupation," he said.
Egypt, the United States and Qatar have scheduled a new round of ceasefire negotiations for Thursday, as fears grow of a broader conflict involving Iran and its Lebanese ally Hezbollah.
Israeli Prime Minister Benjamin Netanyahu, who has said he will not end the war until Hamas no longer poses a threat to Israelis, said he would send a delegation.
Israel launched its assault on Gaza after Hamas fighters stormed into southern Israel on Oct. 7, killing 1,200 people, mostly civilians, and capturing more than 250 hostages, according to Israeli tallies.
Since then, nearly 40,000 Palestinians have been killed in the Israeli offensive in Gaza, according to the health ministry, which does not distinguish between combatants and civilians.
Health officials say most of the fatalities have been civilians but Israel says at least a third are fighters. Israel says it has lost 329 soldiers in Gaza, while Iran-backed Hamas does not publish its casualties.
