Chris Gunness, Unrwa spokesman: 'We've had no other choice'
The UN's main aid agency has suspended its operations in Gaza because its staff have been hit by Israeli attacks.
The suspension would continue "until the Israeli authorities can guarantee our safety and security", the UN said.
Meanwhile, the US, UK and France have dropped opposition to a UN resolution urging an immediate ceasefire, and Arab nations are studying a draft.
It comes on day 13 of an offensive by Israel aimed at stopping Palestinian militants firing rockets from Gaza.
The US, UK and France had wanted a weaker statement from the 15-nation UN Security Council, the BBC's Laura Trevelyan in New York says.
But Arab foreign ministers said anything less than a binding resolution calling for an immediate ceasefire would be an inadequate response to the crisis, our correspondent says.
If the Arab nations' response to the draft resolution is positive, a vote could happen later.
The draft calls for an immediate ceasefire, action to stop the smuggling of arms by Hamas across the Egypt-Gaza border and the opening of border crossings into Gaza so aid can be delivered.
At least 765 Palestinian lives are said by sources in Gaza to have been lost since the offensive began 13 days ago.
Three more Israeli soldiers were killed in Thursday, bringing Israel's death toll to 11 military personnel and three civilians.
A captain and a sergeant were shot dead in separate clashes while a major was killed by an anti-tank missile, Israeli newspaper Haaretz reports.
Responding to the suspension of aid efforts by the UN relief agency Unrwa, Israeli government spokesman Mark Regev said Israel fully supported the work of the UN and other humanitarian agencies in Gaza.
"We will do what needs to be done to facilitate this vital work," he said. "In these difficult days we must work together to meet the humanitarian needs of the population."
Our installations have been hit, our workers have been killed in spite of the fact that the Israeli authorities have the co-ordinates of our facilities
Unrwa's move came shortly after it said one person had been killed and two hurt when a fork-lift truck on a UN aid mission came under Israeli tank fire at Gaza's Erez crossing.
It said it was "with great regret" that it had been forced to make a difficult decision.
"We have suspended our operations in Gaza until the Israeli authorities can guarantee our safety and security," said Unrwa spokesman Chris Gunness.
"Our installations have been hit, our workers have been killed in spite of the fact that the Israeli authorities have the co-ordinates of our facilities and that all our movements are co-ordinated with the Israeli army."
The UN said the movements of the truck hit at the Erez crossing had been co-ordinated and cleared with the Israeli military.
The Israeli army has not commented on that claim but has said it is looking into the matter.
In a statement, UN Secretary General Ban Ki-moon condemned the Israeli military's action.
John Ging, director of operations in Gaza for Unrwa, said a convoy of two UN vehicles and an ambulance had also been fired at - although it was not clear by whom - despite having clearance for its movements from Israel.
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