The agency supporting more than 800,000 displaced people in the Israeli-besieged Gaza Strip said many of its services had already been shuttered including dozens of water wells, two water plants and sewage pumping stations.

"I do believe there is a deliberate attempt to strangle our operation and paralyse the operation," UNRWA Commissioner-General Philippe Lazzarini told journalists in Geneva.

"We run the risk to have to suspend the entire humanitarian operation," he said. "I do believe that it is outrageous that humanitarian agencies have been reduced to begging for fuel."

Lazzarini said the organisation had pleaded for weeks for access to fuel, which on Wednesday was carried into Gaza for the first time since the start of Israel's war with Hamas.

That fuel - 24,000 litres (6,340 gallons) of diesel fuel for U.N. aid distribution trucks - is nowhere near what Gazans need to survive, Lazzarini said.

"Because of the lack of fuel, we will not be able to send our trucks across the south of the Gaza Strip where we have people waiting for humanitarian deliveries," he said, referring to the Rafah crossing with Egypt, the only one open for aid deliveries.

Israel refuses fuel imports, saying it could be used by Hamas for military purposes.

Without fuel, Lazzarini warned, civilian deaths that are not directly linked to Israel's retaliatory military campaign against Hamas for its Oct. 7 attacks were inevitable.

"Today what we are saying is if the fuel does not come in, people will start to die because of the lack of fuel. Exactly as from when, I don’t know. But it will be sooner rather than later," he said.

Gaza's main telecommunications companies, Paltel (PALTEL.PL) and Jawwal, said on Thursday that all telecom services in the densely populated enclave had gone out as all energy sources have been depleted.

"It can provoke or accelerate (the breakdown of) last remaining civil order we have in the Gaza Strip," Lazzarini said of the blackout, calling the scale of loss and destruction in Gaza "just staggering."