As Israel warns more Gaza neighborhoods to evacuate, a top U.N. envoy told the United Nations Security Council on Thursday that Israel would be required under international law to take responsibility for helping Palestinians civilians in any further large-scale displacements.

The United Nations is struggling to cope with a flood of some 220,000 Palestinian civilians into shelters. They have come under fire during three weeks of fighting between Israel and Hamas militants who dominate Gaza.

Speaking from Gaza City, Pierre Krähenbühl, head of the U.N. Relief and Works Agency (UNRWA), said the impoverished enclave of 1.8 million Palestinians was facing a precipice. Krähenbühl said he was alarmed to hear that Israel had warned more neighborhoods in Gaza to evacuate ahead of military action.

"Should further large-scale displacement indeed occur, the occupying power, according to international humanitarian law, will have to assume direct responsibility to assist these people," he told the 15-member Security Council.

"With as many as 2,500 displaced people residing in (each U.N.) school and an average of 80 people to a classroom, we have exceeded the tolerable limits we can accommodate," he said.

According to the Geneva Conventions on the conduct of war and occupations, an occupying power must "to the fullest extent of the means available to it" ensure public health, hygiene, food and medical supplies for the civilians under occupation.

Eight U.N. employees have been killed since Israel launched its offensive on July 8. Dozens of people have been killed in attacks on U.N. schools sheltering civilians, while caches of rockets have been found in vacant U.N. schools in Gaza on three occasions.

"The reality of Gaza today is that no place is safe," U.N. aid chief Valerie Amos told the U.N. Security Council. "We have all watched in horror the desperation of children, of civilians as they have come under attack."

She said 80 percent of the more than 1,300 Palestinians killed were civilians, including 251 children, while three Israeli civilians and 56 Israeli soldiers had died. Amos said nearly a quarter of the Palestinian population were displaced.

"The relief effort is stretched," Amos said. "Until a longer-term ceasefire is agreed, we need more humanitarian pauses to enable us to reach those in need."

Palestinian U.N. Ambassador Riyad Mansour accused Israel of carrying out a genocide, while Israeli U.N. Ambassador Ron Prosor accused Islamist Hamas militants - blacklisted as a terrorist group by many Western countries - of using civilians as human shields.

"When you put 1.8 million Palestinian civilians in this huge prison, denying them food ... denying them electricity, denying them safe places, denying them adequate medical facilities, denying them clean water - what are you doing? Isn't that genocide?" Mansour told reporters.

Prosor described the humanitarian situation as troubling and said Israel was "genuinely concerned for the wellbeing of the Palestinian people."

*This story was edited by Ahram Online.