The United States has called on Israel to be "fully" transparent about the strike.

"The government of Israel has said that they are going to release more information about this strike, including the names of those who died in it. We expect them to be fully transparent in making that information public," State Department spokesman Matthew Miller told reporters.

UN chief Antonio Guterres called the strike "just another horrific example of the price that civilians are paying".

"There will need to be accountability for everything that has happened in Gaza," his spokesman Stephane Dujarric said.

EU foreign policy chief Josep Borrell called for the strike to be "independently investigated".

Israel accuses Hamas and its allies in Gaza of using schools, hospitals and other civilian infrastructure including facilities run by UNRWA, the UN agency for Palestinian refugees, as operational centres -- charges the militants deny.

The Al-Aqsa Martyrs hospital in Deir al-Balah, near Nuseirat, said it had received the bodies of at least "37 martyrs" from the strike.

Faisal Thari, a displaced Gazan who had sought refuge at the school, told AFP: "Why? What have we done for them to bomb us?"

Hamas in a statement decried a "new crime... against our people".

A medic said another Israeli pre-dawn strike killed six people in a house in Nuseirat refugee camp, and witnesses reported intense shelling in the Bureij and Al-Maghazi camps in the same area.

Israeli warplanes also carried out strikes in parts of Rafah, a source in Gaza's southernmost city told AFP.

The military said a soldier was killed in Gaza on Thursday, bringing to 295 the death toll since its ground offensive in the Palestinian territory began on 27 October.

The war was sparked by Hamas's 7-October attack, which resulted in the deaths of 1,194 people, mostly civilians, according to an AFP tally based on Israeli official figures.

Militants also took 251 hostages, 120 of whom remain in Gaza, including 41 the army says are dead.

Israel's retaliatory military offensive has killed at least 36,654 people in Gaza, also mostly civilians, according to the Hamas-run territory's health ministry.

Israel has faced growing diplomatic isolation, with international court cases accusing it of war crimes and several European countries recognising a Palestinian state.

Spain, which last week sparked Israeli fury by formally recognising Palestinian statehood, said Thursday it would become the latest country to join South Africa's case at the International Court of Justice accusing Israel of "genocide" against Palestinians in Gaza.

Israeli prime minister Benjamin Netanyahu has meanwhile accepted an invitation from lawmakers in the United States, his main ally and military backer, to address Congress on 24 July, a congressional source told AFP.

US President Joe Biden last week outlined what he called a three-phase Israeli plan to halt the fighting for six weeks while hostages are exchanged for Palestinian prisoners in Israeli jails and the delivery of aid into Gaza is stepped up.

G7 powers and Arab states have backed the proposal, and on Wednesday 16 world leaders signed alongside Biden calling for Hamas to accept the deal.

"There is no time to lose. We call on Hamas to close this agreement," said a White House statement.

Egypt's state-linked Al-Qahera news quoted a high-level source Thursday saying that Cairo had "received positive signs from the Palestinian movement signalling its aspiration for a ceasefire".

But Beirut-based senior Hamas official Osama Hamdan on Thursday cast doubt on the proposal, calling it "just words said by Biden in a speech".

Qatar's foreign ministry spokesman said Thursday that Hamas has not yet given its response on the truce plan.

Major sticking points include Hamas insisting on a permanent truce and full Israeli withdrawal -- demands Israel has rejected.

jjjLebanon 'escalation'

The war has sent regional tensions soaring, with violence on the rise involving Israel and its allies on the one hand, and Iran-backed armed groups on the other.

Regular cross-border clashes between Israeli forces and Lebanon's Hezbollah movement, which have forced mass evacuations on both sides, have intensified.

The Israeli military on Thursday announced a soldier was killed in a Hezbollah drone strike the day before on Hurfeish.

Israeli politicians have threatened more intense fighting against Hezbollah, which last fought a major war with Israel in 2006.

Netanyahu was in the occupied West Bank on Thursday, a day after saying Israel was "prepared for a very intense operation" along the border with Lebanon.

"The state of Israel is in a difficult campaign on many fronts," he said at a military command centre.

"This effort is being carried out amid complicated international pressure on us."

The US State Department's Miller has said any "escalation" in Lebanon would "greatly harm Israel's overall security".