Israeli shells struck a UN school in Gaza on Wednesday, killing 16, as ground troops made a signficant push into the territory despite Palestinian efforts to broker a 24-hour truce.
It was the second time in a week that a UN school sheltering hundreds of homeless Palestinians had been hit, with the latest violence pushing the Gaza death toll over 1,270.
The bloodshed came as a top-level Palestinian delegation, including Hamas and Islamic Jihad leaders, was preparing to head to Cairo to discuss a new proposal for a temporary humanitarian ceasefire, a top PLO official said.
But there was no word on whether Israel would respond to the initiative, with the military striking 75 targets in Gaza overnight as ground troops made a "significant advance" inside the narrow coastal enclave, army radio reported.
Violence in Gaza claimed more than 50 lives on Tuesday, with the worst strike taking place at the school in Jabaliya refugee camp in the north where hundreds had been seeking shelter after the army warned them to flee their homes.
So far, UN figures show up to 240,000 people have fled their homes in a territory which is home to 1.7 million Palestinians, leaving one in seven people homeless.
Many have taken shelter at schools run by the UN agency for Palestinian refugees (UNRWA), a number of which have been hit by shells in the past week, although the agency has reported finding rockets stored at at least two of its uninhabited schools.
Two shells struck the Jabaliya school, one hitting a classroom on the ground floor where people had been staying and a second slamming into the top floor, hitting another classroom which was apparently empty, an AFP correspondent said.
Inside the school yard was a makeshift animal pen where several horses and donkeys had been killed by shrapnel, lying in pools of blood as other terrified animals cowered nearby.
Facing onto the yard was a classroom whose wall had been completely destroyed.
Inside, two young men wearing Palestinian boy scout scarves were engaged in the grisly task of collecting bodyparts. With no gloves, their hands were completely stained with blood as the picked up chunks of flesh and put them into thin plastic bags.
- PLO truce proposal -
"They're bombing houses, homes, schools - there's no protection," said Moin al-Athamna, one of those staying at the school, saying everyone had been sleeping when the first shell hit.
"They were all kids in there, young people," said Hisham al-Masri. "Why would they do this? Where can people go?"
An AFP correspondent said the army had been pounding the area with tank fire for an hour prior to the incident.
International efforts to broker an end to the bloody conflict have so far led nowhere, with current efforts focused on a top-level Palestinian delegation which was expected to visit Cairo in the coming days to discuss a new interim truce proposal.
But US efforts were also ongoing, with Secretary of State John Kerry saying Israeli Prime Minister Benjamin Netanyahu had turned to Washington for help trying to broker a ceasefire.
"The prime minister talked to me about an idea and a possibility of a ceasefire. He raised it with me, as he has consistently," Kerry said on Tuesday, adding that Netanyahu had asked for a truce which would allow Israel "to protect itself against the tunnels".
His remarks came after the Palestine Liberation Organisation (PLO) said it had garnered Hamas support for a 24-hour truce which would be discussed in Cairo.
Palestinian president Mahmud Abbas had been in touch with exiled Hamas chief Khaled Meshaal on Monday and Tuesday and had "proposed the 24 hour truce", senior official Nabil Shaath told AFP. "Meshaal and Hamas agreed."
But Hamas said it had not so far agreed to any new truce and was waiting for Israel to show its hand first.
"When we have an Israeli commitment... on a humanitarian truce, we will look into it," spokesman Sami Abu Zuhri said.
- Children paying the price -
And Hamas's military chief Mohammed Deif released an audio statement saying there would be no end to the fighting without Israel lifting its eight-year blockade on Gaza.
"We don't accept any conditions for a ceasefire. There is no ceasefire without the stop of the aggression and the end of the siege."
At least seven children were killed during the morning, among them an 11-year-old disabled girl who died in a shelling in Gaza City, and a 16-year-old girl killed in a strike on central Gaza.
UN figures indicate that nearly three quarters of those killed were civilians and more than a fifth of them children.
In the southern city of Khan Yunis, an early strike killed nine members of one family, and several hours later, tank shelling killed seven members of another family. Another family of seven was killed in a strike on Tuffah in northeastern Gaza City, medics said.
The violence raised Wednesday's death toll to more than 50, with the overall number of people killed in Gaza now standing at 1,283.
On the Israeli side, the conflict has cost the lives of 53 soldiers, all of whom were killed since the ground operation began, as well as two civilians and a Thai worker who were killed by rocket fire.