Fifteen Palestinians were killed Thursday 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 ceasefire.
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 down in the middle of the courtyard 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 ceasefire plan.
Hamas has so far refused all ceasefire efforts, with its exiled leader Khaled Meshaal vowing late 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 Mahmud Abbas from Ramallah to Amman for urgent talks with Jordan's King Abdullah II, the presidency said.
- Khuzaa under fire -
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.
Although UNRWA did not immediately give its own toll, spokesman Chris Gunness said there were "multiple dead and injured" after an Israeli tank shell hit a UN school being used as a shelter.
AFP's correspondent saw nine bodies, including that of a year-old baby and his mother at a nearby morgue.
"We've spent much of the day trying to negotiate or to coordinate a window so that civilians, including our staff, could leave," Gunness said.
"That was never granted... and the consequences of that appear to be tragic."
With the schoolyard now deserted, a few sheep and goats could be seen wandering around looking for their owners who had all been evacuated to a nearby hospital, an AFP correspondent said.
In response, the Israeli army pledged to open an investigation.
"First of all, we need to investigate what happened there," General Micky Edelstein, commander of the army's Gaza division told reporters.
But the army also accused militant groups of deliberately firing from densely-populated areas, saying they were "using civilian infrastructure and international symbols as human shields".
It also suggested the casualties may have been caused by "several rockets launched by Hamas (which) landed in the Beit Hanun area."
- A heavy civilian toll -
The Gaza-based Palestinian Centre for Human Rights has said more than 80 percent of the casualties so far have been civilians, and a quarter of them children, triggering growing international alarm over the civilian body count.
"We are gravely concerned by the ongoing heavy level of civilian causalities," British Foreign Secretary Philip Hammond said at a press conference in Jerusalem before flying to Cairo for talks with Egyptian President Abdel Fattah al-Sisi.
And UN humanitarian chief Valerie Amos also expressed deep concern about the mounting civilian casualties in Gaza, telling BBC radio that it was "almost impossible" for Palestinians to shelter from Israeli airstrikes.
"It doesn't matter how hard Israel tries to minimise harm, this is an extremely overcrowded stretch of land.
"No one is denying the right of Israel to defend itself but there are huge concerns about the impact this is having on ordinary people on the ground."
Meanwhile, US airlines on Thursday lifted a two-day ban on flights to Israel, with other international airlines expected to follow suit.
The ban was put in place on Tuesday after a rocket hit a house very close to the runways, with Hamas hailing the suspension of Tel Aviv flights as a "great victory."
So far, 32 Israeli soldiers and three civilians have died in the fighting, one of whom was a Thai farm labourer who was killed when a rocket struck the greenhouse where he was working in southern Israel.
Bangkok has demanded Israel "immediately" relocate 4,000 Thai nationals working in the Gaza periphery.