Two babies have died and dozens more are at risk at Gaza's largest hospital after it ran out of power, Palestinian officials have said.
Another patient in intensive care was killed in Israeli shelling that hit the al Shifa hospital in Gaza, the strip's Hamas-run health ministry said.
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The hospital has had to suspend all operations after it ran out of fuel, spokesperson Ashraf al Qidra said.
It comes as Israeli Prime Minister Benjamin Netanyahu rejected growing international calls for a ceasefire in Gaza, saying Israel's battle to crush Hamas militants will continue with "full force".
People in cities across the world, including in the UK, marched on Saturday, calling for a ceasefire - which Mr Netanyahu has rejected and a number of Western governments - including those in the US and UK - have said will allow Hamas to regroup.
A ceasefire would be possible only if all 239 hostages held by Hamas in Gaza are released, Mr Netanyahu said in a televised address on Saturday.
Hamas says it does not use hospitals in this way and medical staff have repeatedly denied Israel's claims.
Israeli authorities have called for doctors, patients and thousands of evacuees who have taken refuge at hospitals in northern Gaza to leave amid intense shelling and fighting.
Most of those sheltering in al Shifa hospital have fled but around 500 patients remain with medical staff saying they will die if they are moved.
Israel said on Saturday it was ready to evacuate babies from the facility.
Palestinian officials said on Friday 11,078 Gaza residents - around 40% of them children - had been killed in air and artillery strikes since the 7 October attacks, which Israel said resulted in 1,200 people being killed and more than 200 taken hostage.
Meanwhile, three Palestinians were killed by Israeli forces in the West Bank on Saturday, the Palestinian health ministry said.
One of those killed was from the town of Jenin while the others were from Arraba, a town to the southwest.
Patients have 'started to die'
Mohammed Abu Selmia, director of al Shifa hospital said: "There is no electricity. Medical devices stopped. Patients, especially those in intensive care, started to die."
Speaking by phone over the sound of gunfire and explosions, he added that Israeli troops are "shooting at anyone outside or inside the hospital" and have prevented movement between the buildings in the compound.
But the former Israeli ambassador to the UK, Mark Regev, cast doubt on the accuracy of reports from hospital doctors, saying: "Ultimately, the hospital has been turned into a military site. There is Hamas's key command and control, and from there, there is a network of tunnels going literally for kilometre after kilometre after kilometre underground as part of their subterranean terror machine."
When questioned why Israel had not released evidence of Hamas using the hospital as a military base, Mr Regev told Sky News it would be forthcoming.
So far, more than 150,000 civilians have fled the north, according to UN monitors. Although tens of thousands remain - many sheltering at hospitals and UN facilities.
Mr Netanyahu also insisted that after the war, which is now entering its sixth week, Gaza would be demilitarised and Israel would retain security control there.
Such a position is at odds with the post-war scenarios floated by Israel's closest ally, the US, which has said it opposes an Israeli reoccupation of the territory.
As the fighting continues, Hamas said it had completely or partially destroyed more than 160 Israeli military targets in Gaza, including more than 25 vehicles in the past 48 hours.
But an Israeli military spokesperson said Hamas had lost control of northern Gaza.
Meanwhile, in Lebanon, the head of the powerful Hezbollah party said that its armed wing had used new types of weapons and struck new targets in Israel, and pledged that the front against its sworn enemy would remain active.
At an extraordinary joint Islamic-Arab summit in Riyadh, Saudi Arabia and other Muslim countries called for an immediate end to military operations in Gaza and rejected Israel's justification of its actions against Palestinians as self-defence.
It also urged the International Criminal Court to investigate "war crimes and crimes against humanity that Israel is committing" in the Palestinian territories.
The president of the Palestinian Authority, Mahmoud Abbas, said Palestinians were facing an "unmatched genocidal war".
Turkey's President Tayyip Erdogan said that an international peace conference should be convened to find a permanent solution to the conflict.
Israel's allies have backed the country's right to defend itself, but pressure is growing on Israel to do more to protect Palestinian civilians.