The UN agency providing aid to Palestinian civilians in besieged Gaza warned it may have to shut down operations shortly if no fuel reaches the enclave, amid an increasingly desperate need for shelter, water, food, and medical services.

The UN agency for Palestinian refugees (UNRWA) said it urgently needed fuel to maintain life-saving humanitarian operations in the Islamist Hamas-ruled enclave that has been under Israeli bombardment for almost three weeks.

"If fuel is not received into Gaza, UNRWA will be forced to significantly reduce and in some cases bring its humanitarian operations across the Gaza Strip to a halt. The coming 24 hours are very critical," it said.

Israel has refused to let in fuel with aid shipments, saying it could be seized by Hamas.

More than 613,000 people made homeless by the war between Israel and Iran-backed Hamas are sheltering in 150 UNRWA facilities across the shattered territory, one of the world's most densely populated places.

"In the last 24 hours another three UNRWA staff members have been killed, bringing the total to 38 staff killed," said UNRWA.

The enclave is reeling from unrelenting Israeli air strikes, triggered by a deadly cross-border rampage into southern Israeli communities by Hamas militants on October 7.

Israel says the Hamas operation killed some 1,400 people. Gaza's health ministry said on Thursday that more than 7,028 Palestinians had been killed in air strikes since then.

The death toll is likely to rise if Israel launches a widely expected ground offensive aimed at annihilating Hamas, whose fighters it says are enmeshed in the population as cover.

Palestinians in Gaza said air strikes had pounded the territory again overnight and people living in its central area, near the Bureij refugee camp and east of the village of Qarara, reported intensive tank shelling before daybreak.

Around midday on Thursday, according to officials at Nasser Hospital in the southern town of Khan Younis, Israel bombed an area not far from an UNRWA shelter for displaced people, killing at least 18 people and causing panic among the displaced.