Palestinian officials said 65 Palestinians, at least 15 of them under the age of 18, had been killed since Israel sent ground forces on Thursday into the densely-populated enclave of 1.8 million Palestinians.
In all, 307 Palestinians have been killed since fighting began on July 8, Gaza officials said. Most of the dead were civilians, of whom more than 50 were under the age of 18. About 2,260 other people have been injured.
The US president, Barack Obama, said on Friday he had spoken to Benjamin Netanyahu, the Israeli prime minister, about "the risks of further escalation" and the loss of innocent lives
However, he emphasised Washington's support for Israel to defend itself, Al Jazeera reported.
"We are hopeful that Israel will continue to approach this process in a way that minimises civilian casualties," Obama said.
Meantime, Palestinian Hamas movement said its men were hitting Israeli tanks with mortar rounds and setting off bombs against troops crossing under smokescreens.