Israeli forces reached the gates of Gaza City's main hospital, the primary target in their battle to seize control of the northern half of the Gaza Strip, where medics said patients including newborn babies were dying for lack of fuel.

There was also fresh concern that the war could spread beyond Gaza, with an upsurge of clashes on Israel's northern border with Lebanon, and the United States launching air strikes on Iran-linked militia targets in neighbouring Syria.

Israel launched its campaign last month to annihilate Hamas, the militant group which runs the Gaza Strip, after Hamas fighters rampaged through southern Israel killing civilians. Around 1,200 people died and 240 were dragged to Gaza as hostages according to Israel's tally, in the deadliest day in its 75-year history.

Since then thousands of Gazans have been killed and more than half of the population made homeless by a relentless Israeli military campaign. Israel has ordered the total evacuation of the northern half of Gaza. Gaza medical authorities say more than 11,000 people have been confirmed killed, around 40% of them children.

Israeli ground forces entered Gaza in late October and have quickly encircled Gaza City, the main settlement in the north. Fighting has since been concentrated in a tightening circle around the Shifa hospital, the enclave's biggest, where thousands of civilians sought shelter.

Israel says Hamas fighters have an underground headquarters in tunnels beneath the hospital and are deliberately using its patients as a shield, which Hamas denies.

Gaza health ministry spokesperson Ashraf Al-Qidra, who was inside the Al Shifa hospital in Gaza city, said an Israel tank was now stationed at the hospital gate.

"The tank is outside the gate of the outpatient clinic department, this is how the situation looks this morning," Qidra told Reuters by phone.

Israel has told civilians to leave and medics to send patients elsewhere. It says it has attempted to evacuate babies from the neo-natal ward and left 300 litres of fuel to power emergency generators at the hospital entrance, but the offers were blocked by Hamas.

Qidra, the Gaza health ministry spokesperson, denied rejecting the offers of fuel but said the 300 litres would power the hospital for just half an hour. Shifa needed 8,000-10,000 litres of fuel per day, which must be delivered by the Red Cross or an international aid agency, he told Reuters.

An Israeli official who requested anonymity said 300 litres could last several hours because only the emergency room was now operating, reducing the hospital's need for fuel.

The Gaza health ministry said that of 45 babies in incubators at Shifa, three had died as of Sunday. Qidra had no immediate update.

A surgeon at the hospital, Dr Ahmed El Mokhallalati, said on Sunday bombing had forced staff to line up premature babies on ordinary beds, using the little power available to run warm them.

"We are expecting to lose more of them day by day," he said.

Al Shifa was "not functioning as a hospital anymore", World Health Organization chief Tedros Adhanom Ghebreyesus said in a post on X.

"Tragically, the number of patient fatalities has increased significantly," he said. "The world cannot stand silent while hospitals, which should be safe havens, are transformed into scenes of death, devastation, and despair."