The largest hospital in Gaza has ceased to function and fatalities among patients are rising, the head of the World Health Organization (WHO) said, as a fierce Israeli assault continues in the Hamas-controlled strip.

According to medical staff of the Al-Shifa complex, three newborns are already dead and more at risk from power outages amid intense fighting as Hospitals in the north of Gaza, including Al Shifa are blockaded by Israeli forces and barely able to care for those inside.

Israel says it is attacking Hamas militants who launched deadly attacks in southern Israel on Oct. 7, and says the group has command centres under and near the hospitals.

The WHO speaking to health officials at Al-Shifa, 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.

Palestinian and UN officials say Gaza's largest hospital is no longer in operation. The director of Al-Shifa Hospital says the facility is out of fuel, leading to the deaths of patients including babies.

Israel says it is trying to free the more than 200 hostages taken by Hamas militants on Oct. 7 and says the hospitals should be evacuated.