Israel hit a Gaza school on Thursday in an airstrike that it said targeted and killed Hamas fighters inside, while a Hamas official said 40 people including women and children were killed as they sheltered in the U.N. site.

The strike took place at a sensitive moment in mediated negotiations on a ceasefire agreement entailing the release of hostages seized by Hamas on Oct. 7 and some of the Palestinians held in Israeli jails. Hamas seeks a permanent end to the war. Israel says it must destroy the Islamist group first.

The United States issued a joint statement with other countries on Thursday calling on Israel and Hamas to make whatever compromises were necessary to finalise a deal as the two sides gave contradictory accounts of the school attack.

Ismail Al-Thawabta, the director of the Hamas-run government media office, rejected Israel’s assertion that the U.N. school in Nuseirat, in central Gaza, had hidden a Hamas command post.

“The occupation uses … false fabricated stories to justify the brutal crime it conducted against dozens of displaced people,” Thawabta told Reuters.

Israel’s military said its fighter jets had carried out a “precise strike” and circulated satellite photos highlighting two parts of a building where it said the fighters were based.

“We’re very confident in the intelligence,” military spokesperson Lt Col. Peter Lerner told a briefing with reporters, accusing Hamas and Islamic Jihad fighters of deliberately using U.N. facilities as operational bases.

He said 20-30 fighters were located in the compound, and many of them had been killed, but had no precise details as intelligence assessments were being carried out. “I’m not aware of any civilian casualties and I’d be very, very cautious of accepting anything that Hamas puts out,” he said.

The school, run by the U.N. Palestinian refugee agency (UNRWA), may have been hit several times, said the agency’s communications director, Juliette Touma.

She said she could not confirm the death toll at this stage. Media in Hamas-run Gaza had earlier put the toll at 35-40. Thawabta and a medical source said 40 had been killed, including 14 children and nine women.

CEASEFIRE EFFORTS

Israel announced a new military campaign in central Gaza on Wednesday as it battles fighters relying on hit-and-run insurgency tactics. It says there will be no halt to fighting during ceasefire talks, which have intensified since U.S. President Joe Biden outlined a proposal on Friday.

Since a week-long truce in November, all attempts to arrange a ceasefire have failed, with each side blaming the other.

“At this decisive moment, we call on the leaders of Israel as well as Hamas to make whatever final compromises are necessary to close this deal,” said the statement issued by the White House jointly with Argentina, Austria, Brazil, Britain, Canada and others.

CIA director William Burns met senior officials from mediators Qatar and Egypt on Wednesday in Doha to discuss the ceasefire proposal. Two Egyptian security sources said talks continued on Thursday but had shown no sign of breakthrough.

Biden has repeatedly declared that ceasefires were close over the past several months, only for no truce to materialise.

Last week’s high-profile announcement coincides with intense domestic political pressure on Israeli Prime Minister Benjamin Netanyahu to chart a path to end the eight-month-old war and negotiate the release of Israeli hostages held by Hamas.

Hamas, which rules Gaza, precipitated the war by attacking Israeli territory on Oct. 7, killing around 1,200 people and capturing more than 250 hostages, according to Israeli tallies. Around half of the hostages were freed in the November truce.

Israel’s military assault on Gaza has killed more than 36,000 people, according to health officials in the territory, who say thousands more dead are feared buried under the rubble.

About half of Hamas’s forces have been wiped out in eight months of fighting and the group is relying on insurgent tactics to frustrate Israel’s attempts to take control of Gaza, U.S. and Israeli officials told Reuters.

Hamas has been reduced to 9,000 to 12,000 fighters, according to three senior U.S. officials familiar with battlefield developments, down from American estimates of 20,000-25,000 before the conflict. Israel says it has lost almost 300 troops in the Gaza campaign.

Hamas does not disclose fatalities among its fighters and some officials have described Israel’s figures for the number of Hamas fighters killed as exaggerated.

Meanwhile, a conflict between Israel and the Lebanon-based Hezbollah is threatening to escalate, with the U.S. State Department warning against a full-blown war.

Although Biden described the ceasefire proposal as an Israeli offer, Israel’s government has been lukewarm in public. A top Netanyahu aide confirmed on Sunday that Israel had made the proposal even though it was “not a good deal“.

Far-right members of Netanyahu’s government have pledged to quit if he agrees to a peace deal that leaves Hamas in place, a move that could force a new election and end the political career of Israel’s longest-serving leader.

Centrist opponents who joined Netanyahu’s war cabinet in a show of unity at the outset of the conflict have also threatened to quit, saying his government has no plan.