Gaza's largest hospital ceased to function and fatalities among patients were rising, the World Health Organization (WHO) said late Sunday, as fierce Israeli assault on the strip continued.

Hospitals in the north of the Palestinian enclave, including the Al-Shifa, were blockaded by Israeli forces and barely able to care for those inside, with three newborns dead and more at risk from power outages amid intense fighting nearby, according to medical staff.

The WHO managed to speak to health professionals at Al-Shifa, who described a "dire and perilous" situation with constant gunfire and bombing exacerbating the already critical situation, Director-General Tedros Adhanom Ghebreyesus said.

"Tragically, the number of patient fatalities has increased significantly," he said in a post on X, formerly known as Twitter, adding that Al-Shifa was "not functioning as a hospital anymore."

Tedros joined other top United Nations officials in calling for an immediate ceasefire.

"The world cannot stand silent while hospitals, which should be safe havens, are transformed into scenes of death, devastation, and despair," he said.

Babies at risk

Israel's military claimed it had offered to evacuate newborn babies and had placed 300 liters of fuel at Al-Shifa's entrance on Saturday night, but both gestures had been blocked by Hamas.

Hamas denied that it refused the fuel and said the hospital was under the authority of Gaza's Health Ministry, adding that the amount of fuel Israel said it offered was "not enough to operate the (hospital's) generators for more than half an hour."

Ashraf Al-Qidra, spokesperson for the Health Ministry, said that of 45 babies in incubators at Al-Shifa, three had already died.

A plastic surgeon in Al-Shifa said the bombing of the building housing incubators had forced staff to line up premature babies on ordinary beds, using the little power available to run the air conditioning to warm.

"We are expecting to lose more of them day by day," said Dr. Ahmed el Mokhallalati.

The Palestinian Red Crescent said the strip's second largest hospital, Al-Quds, was also out of service, with staff struggling to care for those already there with little medicine, food and water.

"Al Quds hospital has been cut off from the world in the last six to seven days. No way in, no way out," said Tommaso Della Longa, spokesperson for the International Federation of Red Cross and Red Crescent Societies.