Israel said on Thursday it would not pull troops from Gaza until they finish destroying a network of cross-border tunnels, despite sharp United Nations criticism over the civilian death toll.

Speaking at the start of a special cabinet meeting in Tel Aviv, Prime Minister Benjamin Netanyahu said he would not accept any ceasefire that did not allow troops to continue destroying tunnels used by militants for attacking Israel.

"Until now, we have destroyed dozens of terror tunnels and we are determined to finish this mission -- with or without a ceasefire," he said at the start of a special cabinet meeting.

"So I will not accept any (truce) proposal that does not allow the IDF (army) to complete this work for the security of Israel's citizens."

His remarks came after the army confirmed mobilising another 16,000 additional reservists, hiking the total number called up to 86,000. Israel does not say how many troops are currently engaged in the fighting inside the Gaza Strip.

And Washington said it had agreed to restock Israel's dwindling supplies of ammunition, despite increasing international concern over the death toll in Gaza, where more than 1,374 people have been killed in 24 days of violence.

UN figures indicate two-thirds of the victims were civilians. Of that civilian dead, nearly half were women and children.

Following the shelling of a UN school in northern Gaza on Wednesday which killed 16, UN human rights chief Navi Pillay slammed Israel for its attacks on homes, schools and hospitals, accusing it of "deliberate defiance" of international law.

"None of this appears to me to be accidental," she told reporters.

"There appears to be deliberate defiance of obligations that international law imposes on Israel."

The shelling of the school also drew sharp condemnation from UN chief Ban Ki-moon, who described it as "reprehensible", as well as from Washington.

But the Israeli army suggested the deaths may have been the result of a misfired Palestinian rocket.

"What happened is still not clear at this stage," military spokesman General Moti Almoz told army radio.

"It is not clear if the school was hit by fire from IDF soldiers or from Hamas terrorists," he said.


'Tunnel vision'

Despite rising international calls for a halt to the bloodshed, the Israeli security cabinet decided Wednesday to press on with the operation in Gaza just hours after troops had made a significant advance into the narrow enclave.

The Israeli offensive began on July 8 with the aim of ending militant rocket fire, but expanded on July 17 with a ground operation aimed at destroying a sophisticated network of tunnels leading under the border, which Israel has vowed to dismantle.

Major General Sami Turgeman, head of the army's southern command, said Wednesday that the army was "just days" away from completing its mission to destroy the tunnels.

Cabinet ministers were being briefed on the progress of the operation in their first meeting since the ground assault began.

"Israel is trapped on the outskirts of Gaza without an exit strategy and without any ceasefire on the horizon," wrote defence correspondent Alex Fishman in the top-selling Yediot Aharonot.

"Within a few days, Israel is going to have to decide either to push ahead with full force or to pull the troops out."

Despite a heavy death toll in Gaza on Wednesday when 111 Palestinians were killed, including 17 who died in a strike on a crowded market place and another 16 at the UN school, Washington said it had restocked the army's ammunition supplies.

The Pentagon confirmed it had granted an Israeli request for ammunition, including some from a stockpile stored by the US military on the ground in Israel for emergency use by the Jewish state.

Rights group Amnesty International had urged Washington to halt arms supplies to Israel.


'15 hurt in UN school'

Meanwhile, there was no letup in bloodshed with at least 10 Palestinians killed on Thursday, among them two women, raising the overall Palestinian toll to 1,374, medics said.

And another 15 people sheltering in the UN school in Jabaliya refugee camp that was struck on Wednesday were wounded when Israeli warplanes attacked a mosque next door, medics said.

In Israel, 56 soldiers have died and Hamas rocket fire has killed three civilians, two Israelis and a Thai national.

Despite the loss of life, there appeared to be little Israeli appetite for a truce, with a senior official telling Haaretz newspaper that a ceasefire was not even close.

Nevertheless, an Israeli delegation travelled to Cairo late Wednesday to discuss a possible ceasefire with Egyptian officials, an official at the airport told AFP.

Cairo, a key mediator in previous truce negotiations between Israel and Hamas, was also expected to host a Palestinian delegation later this week.