Israeli soldiers have killed several Hamas militants at the outset of a raid on the Al Shifa hospital, where thousands of Palestinian civilians - patients, displaced people and medical staff - have been trapped during weeks of fighting.
Israel said it launched the raid because Hamas has a command centre underneath Al Shifa and uses connected tunnels to conceal military operations and to hold hostages. Hamas denies it.
"Before entering the hospital our forces were confronted by explosive devices and terrorist squads, fighting ensued in which terrorists were killed," the Israeli military said on Wednesday, without specifying exactly where the firefight took place.
Israeli Army Radio said five militants had been killed and that weapons were found inside the Al Shifa compound.
Global calls for a humanitarian ceasefire have mounted in recent days as Al Shifa became the focus of Israel's war on Hamas, and fears grew for the thousands of people trapped there, on the front line of the conflict.
Earlier on Wednesday, Dr Munir al-Bursh, director-general of the health ministry for the Hamas-led administration in Gaza, told Al Jazeera that Israeli forces had raided the western side of the medical complex and believed an explosion occurred inside the hospital.
The surgery and emergency departments were raided first, Mohammed Zaqout, the ministry's director of hospitals, told the broadcaster.
Reuters was unable to independently confirm the situation at Al Shifa.
The Israel Defence Forces (IDF) said: "Based on intelligence information and an operational necessity, IDF forces are carrying out a precise and targeted operation against Hamas in a specified area in the Shifa hospital."
Army spokesman Lieutenant Colonel Peter Lerner told CNN the hospital and compound were for Hamas "a central hub of their operations, perhaps even the beating heart and maybe even a centre of gravity".
The US said on Tuesday that its own intelligence supported Israel's conclusions.
Hamas said on Wednesday that US announcement had effectively given a "green light" for Israel to raid the hospital.
The United States did not support air strikes on hospitals nor firefights inside where there were sick, innocent people, the White House National Security Council said.
Israeli forces have waged fierce street battles against Hamas fighters before advancing into the centre of Gaza City and surrounding Al Shifa.
The Israeli military said two soldiers were killed fighting in the northern Gaza Strip on Tuesday, raising to 48 the confirmed Israeli death toll since the ground offensive began.
Israel has sworn to destroy Hamas in retaliation for the militants' cross-border assault into Israel on October 7.
Israel says Hamas killed 1200 people in the rampage and took more than 240 hostage.
Hamas says 650 patients and 5000 to 7000 other civilians are trapped inside the hospital grounds, under constant fire from Israeli snipers and drones.
Amid shortages of fuel, water and supplies, it says 40 patients have died in recent days.
Thirty-six babies are left from the neonatal ward after three died.
Without fuel for generators to power incubators, the babies were being kept as warm as possible, lined up eight to a bed.
The Israeli military said on Wednesday: "We can confirm that incubators, baby food and medical supplies brought by IDF tanks from Israel have successfully reached the Shifa hospital. Our medical teams and Arabic speaking soldiers are on the ground to ensure that these supplies reach those in need."
Palestinians trapped in the hospital dug a mass grave on Tuesday to bury patients who died and no plan was in place to remove babies despite Israel's incubator offer, said Qidra, Gaza's health ministry spokesman.
Qidra said there were about 100 bodies decomposing inside and no way to get them out.
UN Secretary-General Antonio Guterres was deeply disturbed by the "dramatic loss of life" in the hospitals and called for an immediate humanitarian ceasefire, his spokesman said.
Medical officials in Hamas-run Gaza say more than 11,000 people are confirmed dead from Israeli strikes, about 40 per cent of them children, and countless others were trapped under rubble.
About two-thirds of Gaza's 2.3 million people have been made homeless, unable to escape the territory where food, fuel, fresh water and medical supplies are running out.
