Gaza City, Gaza – A Hamas health official said more than 80 people were killed Saturday in twin strikes on a northern Gaza refugee camp, including a UN school used as a shelter for people displaced by the Israel-Gaza war. Meanwhile, thousands in Israel marched to Jerusalem, calling for the release of hostages.

Social media videos verified by AFP showed bodies covered in blood and dust on the floor of a building, where mattresses had been wedged under school tables in Jabalia, the Palestinian territory's biggest refugee camp.

Israel has vowed to destroy Hamas in response to the October 7 attacks which Israeli officials say killed about 1,200 people, most of them civilians in southern Israel, and saw about 240 people taken hostage.

The army's relentless air and ground campaign has since killed 12,300 people, more than 5,000 of them children, according to the Hamas government which has ruled Gaza since 2007.

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"At least 50 people" were killed in a dawn strike on the UN-run Al-Fakhura school in the camp, which has been converted into a shelter for displaced Palestinians, a health ministry official in Hamas-controlled Gaza told AFP.

According to UN figures, some 1.6 million people have been displaced inside the Gaza Strip by six weeks of fighting. UN humanitarian chief Martin Griffiths denounced the "tragic news of the children, women and men killed".

"Shelters are a place for safety," he posted on X, formerly Twitter. "Civilians cannot and should not have to bear this any longer."

A separate strike Saturday on another building in Jabalia camp killed 32 people from the same family, 19 of them children, the Hamas official said.

The Israeli army did not specifically comment on the strikes but said its troops were expanding operations in Gaza, including in parts of Jabalia.

Israel has told Palestinians to move from north Gaza for their safety, but deadly air strikes continued to hit central and southern areas of the coastal enclave.

On Saturday, hundreds of people fled on foot after the director of Gaza's main hospital said the Israeli army ordered the evacuation of the facility, where some 2,000 people were trapped.

Israel has been pressing military operations inside the hospital, searching for the Hamas operations center it says lies under the sprawling complex – a charge Hamas denies.

A two-day blackout caused by fuel shortages ended after a first delivery arrived from Egypt late Friday, but UN officials continued to plead for a ceasefire, warning no part of Gaza is safe.

A strike on a residential building in southern Gaza killed 26 people, the director of the Nasser hospital in Khan Yunis said.

US President Joe Biden's chief adviser for the Middle East said more fuel deliveries and a potential "significant pause" in the fighting both depend of the release of hostages.

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"The surge in humanitarian relief, the surge in fuel, the pause... will come when hostages are released," Brett McGurk told a security conference in Bahrain.

More than half of Gaza's hospitals are no longer functional due to combat, damage or shortages, and people are waiting four to six hours for half the normal ration of bread.

The military says it has found rifles, ammunition, explosives and the entrance to a tunnel shaft at the Al-Shifa hospital complex, claims that cannot be independently verified.

Israel has not recovered hostages at the hospital but said it found not far away the bodies of two kidnapped women, including a soldier. Those held hostage range from infants to octogenarians, and there has been little information on their fate despite ongoing negotiations mediated by Qatar and Egypt to secure releases.

Waving Israeli flags and placards depicting the hostages, thousands of people reached Jerusalem Saturday on the fifth and final day of a march calling for their release.

Relatives of the missing, who quickly formed the Hostages and Missing Families Forum in the wake of the attacks, have consistently criticized the Israeli government for failing to keep them informed, and say release efforts should be an absolute priority of Israel's military campaign.