On Sunday, the UN chief called for those responsible for the "gross violation of international humanitarian law" to be held accountable. "This madness must stop," Ban Ki-moon said through his spokesperson.

The school in Rafah in southern Gaza was hit in a strike earlier on Sunday, killing at least 10 civilians.

Medics and witnesses said a missile launched by an Israeli aircraft had struck the entrance to the school. Robert Turner, the director of operations for the UN Palestinian refugee agency in Gaza, said preliminary findings had indicated that the blast was caused by an Israeli airstrike near the school.

The building had been sheltering hundreds of Palestinians displaced during Israel's offensive in the Gaza Strip.

Ban said the "Israel Defense Forces have been repeatedly informed of the location of these sites." The IDF announced that it was looking into the attack, which is the second to hit a school in less than a week. Last week, a strike on another UN-run school in the Jabalya refugee camp killed more than a dozen people and injured more than 100.

Meanwhile, Israeli media has reported that most troops have pulled out of Gaza. However, the military has stopped short of calling the move a withdrawal.

"The troops are in the midst of redeployment to other parts of the border," Lieutenant-Colonel Peter Lerner said.

"Indeed we are releasing troops from the front line, but the mission is ongoing," Lerner said. "Ground forces are operating. Air forces are operating."

Hamas to pay 'intolerable price'

In a televised address late on Saturday, Israeli Prime Minister Benjamin Netanyahu said the operation would be reassessed, but warned that Hamas would pay an "intolerable price" if it continued to fire rockets at Israel.

Officials say the offensive is aimed at stopping rocket fire from Gaza into Israel and destroying a tunnel network used by Palestinian militants to carry out attacks within Israeli territory.

More than 1,700 Palestinians, most of them civilians, have died in 27 days of fighting. Nearly 70 Israelis, almost all of them soldiers, have also lost their lives.

hc/mkg (Reuters, AP, AFP)