Fifteen Palestinians were killed when an Israeli shell slammed into a UN-run school where hundreds of civilians had taken refuge, sending the death toll in Gaza soaring to 777, despite world efforts to broker a cease fire.

The strike hit a school sheltering some of the 100,000 Palestinians driven out of their homes in search of a safe haven after weeks of deadly fighting between Israeli troops and Hamas militants.

The shell crashed in the middle of the courtyard on Thursday where people had set up camp, leaving the ground covered in bloodstains.

Gaza’s emergency services said 15 people had been killed and more than 200 injured in the school strike, sending the Palestinian death toll from 17 days of fighting to 777.

Meanwhile in Cairo, US Secretary of State John Kerry sought to further regional efforts to broker an end to the bloodshed, reaching out to Turkey and Qatar, both allies of Hamas.

The US diplomat is seeking to garner support for an Egyptian-drafted proposal, with an official saying he had spoken to his counterparts in Doha and Ankara in the hope they would use their influence to encourage Hamas to accept a cease fire plan.

Hamas has so far refused all cease fire efforts, with its exiled leader Khaled Meshaal vowing late on Wednesday there would be no end to the fighting without an end to Israel’s eight-year blockade on Gaza.

Meanwhile, a Jordanian helicopter flew Palestinian President Mahmoud Abbas from Ramallah to Amman for urgent talks with Jordan’s King Abdullah II, the presidency said.

There was no let-up to the violence in Gaza, however, with most of Thursday’s 82 victims killed in and around Khuzaa, a flashpoint area east of Khan Yunis which has been the site of intensive fighting since Tuesday.

Gaza’s health ministry issued a call for international protection for civilians in the area, with the Red Cross saying anyone leaving home was being targeted by Israeli fire.

On Wednesday, the Red Cross and Palestinian ambulances managed to evacuate 150 people from the area following negotiations with both sides, and another convoy of 10 ambulances pulled out another eight bodies and 92 wounded on Thursday, the ICRC said.

But the biggest single strike was at the school in the north, where the UN agency for Palestinian refugees (UNRWA) said it had been trying to coordinate with the army over the evacuation of civilians, without success.

The Israeli army has pledged to open an investigation.