Israeli soldiers evacuate their wounded comrades at an army deployment area near Israel’s border with the Gaza Strip, on July 20, 2014.

GAZA — Gazan authorities said Israeli forces shelled a shelter at a U.N.-run school on Thursday, July 24, killing at least 15 people as the Palestinian death toll in the conflict climbed over 760 and attempts at a truce remained elusive.

Three Israeli soldiers were killed on Wednesday, raising the number of Israeli military fatalities since the operation commenced to 32, as of Thursday. 

United Nations Secretary-General Ban Ki-moon expressed his horror at the attack on the school at Beit Hanoun in the northern Gaza strip. “Many have been killed – including women and children, as well as U.N. staff,” he said in a statement. “Circumstances are still unclear. I strongly condemn this act.”

Ban later arrived to Cairo where he was expected to meet U.S. Secretary of State John Kerry, who has been working the telephones to try to broker an elusive truce.

The Israeli military said it was investigating the incident.

Pools of blood lay on the ground and on students’ desks in the courtyard of the school near the apparent impact mark of the shell, according to a Reuters photographer at the scene.

Scores of crying families who had been living in the school ran with their children to a hospital where the victims were being treated a few hundred meters away. Laila Al-Shinbari, a woman who was at the school when it was shelled, told Reuters that families had gathered in the courtyard expecting to be evacuated shortly in a Red Cross convoy.

“All of us sat in one place when suddenly four shells landed on our heads … Bodies were on the ground, (there was) blood and screams. My son is dead and all my relatives are wounded including my other kids,” she wept.

Ashraf al-Qidra, spokesman for the Gaza Health Ministry, said that as well as the 15 dead, 200 people had been wounded in the attack. The director of a local hospital said various medical centres around Beit Hanoun were receiving the wounded.

“It’s clear that civilians are paying an unimaginable price caught between both sides,” said U.N. Relief and Works Agency (UNRWA) spokesman Chris Gunness. “We were attempting to arrange a window for evacuation for the civilians with the Israeli army that never came. The consequences were deeply tragic.”

Hamas leader Khaled Meshaal said on Wednesday his fighters had made gains against Israel and voiced support for a humanitarian truce, but only if Israel eased restrictions on Gaza’s 1.8 million people. Hamas wants Egypt to open up its border with Gaza too.

Israel has lost at least 32 soldiers in clashes inside Gaza and with Hamas raiders who have slipped under the fortified frontier in tunnels.

Palestinian rockets and mortar bombs have also killed three civilians in Israel. 

Though Israel’s Iron Dome rocket interceptor has shot down most of the rockets fired from Gaza, one that came close to Tel Aviv’s Ben Gurion Airport on Tuesday prompted the U.S. Federal Aviation Administration (FAA) to bar American flights there.

An ensuing wave of cancellations by foreign airlines sharply reduced traffic at Israel’s usually bustling international gateway at the height of the summer tourist season. It was hailed as a victory by Hamas and prompted Israeli Prime Minister Benjamin Netanyahu to appeal to the Obama administration to intervene.

The FAA cancelled the ban late on Wednesday after reviewing the security situation. The European Air Safety Agency (EASA) said on Thursday it was about to follow suit and lift its own recommendation to avoid flying to Tel Aviv.

US Airways, a unit of American Airlines Group Inc, said it was resuming its non-stop Tel Aviv to Philadelphia service. Germany’s Lufthansa said its suspension of flights to Tel Aviv would continue to Friday.

Gaza militants continued to fire rockets at Israel on Thursday, sending thousands in the country’s south racing to shelters or safe rooms. There were no reported casualties.

U.N. High Commissioner for Human Rights Navi Pillay said on Wednesday that there was “a strong possibility” that Israel was committing war crimes in Gaza, where medical officials say most of those killed were civilians.

Pillay also condemned indiscriminate Islamist rocket fire out of Gaza, and the U.N. Human Rights Council said it would launch an international inquiry into alleged violations.

A furious Netanyahu denounced the inquiry as a “travesty.”

“The HRC should be launching an investigation into Hamas’s decision to turn hospitals into military command centres, use schools as weapons depots and place missile batteries next to playgrounds, private homes and mosques,” he said.

Palestinians in the West Bank demonstrated in solidarity with Gaza, as President Mahmoud Abbas backed calls by Hamas for an end to the economic blockade of the Gaza Strip as a condition for a ceasefire.

Two Palestinians were killed Thursday night in clashes between thousands of demonstrators and police in East Jerusalem.

Dozens were reported wounded, seven of them seriously.