Most hospitals in Gaza have already ceased functioning due to bombardments and supply shortages after more than three months of an Israeli offensive prompted by Hamas' deadly attacks on Oct. 7. The Nasser Hospital in Khan Younis, central Gaza, is only minimally functional and is surrounded by Israeli military, the United Nations has said.

"The situation around Nasser has only gotten worse - the shooting, fighting around, the difficulty of access for people to reach Nasser or the difficulty for leaving," WHO spokesperson Christian Lindmeier told a Geneva briefing.

The hospital is sheltering thousands of displaced people as well as medics and patients.

The WHO said that a food shipment intended for the hospital was mobbed on Tuesday by hungry crowds due to delays near an Israeli checkpoint and never reached the facility.

Another WHO fuel delivery for Nasser on Monday was not granted permission, although a medical shipment did arrive, Lindmeier said.

"Denials and delays are part of a pattern which impede humanitarian supplies from reaching hospitals and could make them non-functional," he said.

Previously the main hospital was the Al-Shifa hospital in heavily-damaged northern Gaza which was raided by Israeli troops and eventually evacuated. Some of the patients were transferred southwards and Nasser Hospital has more than three times its intended patients, the United Nations has said.

Describing Nasser as a "crucial symbol", Lindmeir said sometimes surgeries were being performed on its floors.

The WHO has previously said half the medical staff had fled and that just two doctors out of an original 24 remained there.

Lindmeier repeated a WHO call for donors to keep financing the U.N. Palestinian agency (UNRWA) after many countries halted funding following allegations that some staff had taken part in the Oct. 7 attacks.

"It's a distraction. And as important as this discussion is, let's not forget what the real issues are on the ground," he said, alluding to the scale of human suffering in Gaza.