Fighting at the hospital comes as Israel faces growing international pressure to show restraint, after vowing to press its offensive into Rafah, the last relatively safe place in Gaza.
Attacks that have destroyed the majority of Gaza’s medical facilities have caused particular concern, including Israeli raids on hospitals in other cities, shelling in the vicinity of hospitals and the targeting of ambulances.
As massive bombardment destroyed swathes of residential districts and forced most people from their homes, hospitals quickly became the focus for displaced people seeking shelter around buildings they thought more likely to be safe.
Israel accuses Hamas of regularly using hospitals, ambulances and other medical facilities for military purposes, and has aired footage taken by its troops that it says shows tunnels containing weapons below some hospitals.
The Israeli military said it apprehended various suspects at the Nasser Hospital and that its operations there were continuing.
Senior Hamas official Sami Abu Zuhri said Israel was lying about Nasser as it had about other hospitals.
Video shows hospital chaos
Speaking about the hospital raid, Israeli military spokesperson Rear Admiral Daniel Hagari said “this sensitive operation was prepared with precision and is being conducted by IDF special forces who underwent specified training”.
One objective of the operation was to ensure the hospital could continue treating Gazan patients and “we communicated this in a number of conversations we had with the hospital staff,” he said, adding there was no obligation to evacuate.
Gaza health ministry spokesperson Ashraf al-Qidra said Israel had forced doctors at Nasser hospital to abandon patients in intensive care.
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Videos that Reuters verified on Thursday as having been filmed inside Nasser Hospital – though it could not check when – showed chaos and terror.
Men walked through corridors using phone lights, with plaster dust swirling around and debris lying about, at one point wheeling a bed through a damaged area.
In one video, gunshots rang out and a doctor shouted: “Is there anyone still inside? There is gunfire, there is gunfire – heads down”.
Another man in a video said the Israeli army had surrounded the hospital and nobody could get out.
Mohammad al Moghrabi, who had been sheltering in the compound, said some people who attempted to leave on Wednesday were shot at and so returned to the hospital.
“This morning they said there was a safe passage, so we left, but it wasn’t safe. They approached us with a bulldozer and a tank, they insulted us and left us for four hours under the sun.”
The World Health Organisation has previously said half the Nasser medical staff had already fled.
Israel said its forces had killed “a number of terrorists” in central Gaza and Khan Younis in the past 24 hours, including some 15 Hamas fighters in Gaza City.