Thirty-one premature babies were evacuated from Gaza's biggest hospital on Sunday, the World Health Organization said, seeking to get the last patients and staff out of what it has dubbed a "death zone".

The evacuation came as Israel, which said it was stepping up military operations against Hamas militants, announced it had found a 55-metre tunnel under the Al-Shifa hospital while mediator Qatar said "minor" obstacles remained for a deal on the release of hostages.

Sirens blared across Jerusalem to warn of rocket fire from Gaza, sending civilians scurrying for cover as loud blasts from intercepted missiles pierced the air.

In Gaza, a lack of fuel to power incubators has previously led to the deaths of other newborns at Al-Shifa hospital, according to the Hamas-run health ministry.

Al-Shifa has become the focus of the six-week-old war that began October 7 when Gaza-based Hamas militants stormed across the militarised border to kill, according to Israeli officials, around 1,200 people and take roughly 240 hostages.

In Gaza, the Hamas government says the death toll from Israel's relentless aerial bombardment and ground operations, in retaliation for the worst-ever attack against the country, has reached 13,000.

Most of the casualties on both sides are civilians, and include, according to Hamas officials, 5,500 children.

The Israeli army on Sunday said five more soldiers had been killed, raising the number of troop deaths in Gaza to 64.

WHO chief Tedros Adhanom Ghebreyesus said 31 "very sick" babies were moved in a joint operation with staff from the UN and the Palestinian Red Crescent Society (PCRS), which used six ambulances in the transfer.

"They are receiving urgent care in the neonatal intensive care unit" of the Al-Helal Emirati field hospital in Rafah, across the border from Egypt, he wrote on X, formerly Twitter. 

An AFP photographer saw the tiny infants at the hospital, some three or four to a cot, being bottle-fed by nurses and tended to by doctors.

- Hospitals stretched - 

Israel said Saturday its military was "expanding its operational activities in additional neighbourhoods... of the Gaza Strip" where the United Nations says about 1.6 million people have been internally displaced by weeks of fighting.

The narrow coastal territory, under a crippling blockade since Hamas took power in 2007, has been besieged by Israel since the war erupted, leaving food, water, medicine and fuel in short supply.

And more than half of Gaza's 36 hospitals are non-functioning by shortages, combat or damage, the UN says.

France on Sunday said it was sending a navy helicopter carrier to provide medical assistance in Gaza.

On Saturday, hundreds fled Al-Shifa Hospital on foot as loud explosions were heard around the complex. Columns of sick and injured were seen leaving with displaced people, doctors and nurses.

At least 15 bodies, some in advanced stages of decomposition, were strewn along the route, an AFP journalist said.

The WHO said 29 patients at the hospital with serious spinal injuries cannot move without medical assistance.

Israel has told Palestinians to move south for their safety, but deadly strikes continued there too.

On Sunday 41 members of one family were killed in an Israeli bombardment of their home in Gaza's Zeytoun district, the Hamas-run health ministry said.

- 'Extreme suffering' -

Israeli troops raided Al-Shifa Hospital Wednesday on suspicion that it was being used as a Hamas base.

On Sunday the army said "troops exposed a 55-meter-long terror tunnel 10 metres deep underneath the Shifa hospital complex," which ran under the hospital and ended at a blast door.

Israel has been under pressure to prove its allegations that a Hamas command centres is concealed beneath the hospital, a charge the militants and medical staff have denied.

Conditions at Al-Shifa are dire, according to the WHO, with a mass grave outside and nearly 300 patients and 25 health workers inside.

It warned that nearby facilities were already overstretched and urged an immediate ceasefire given the "extreme suffering of the people of Gaza".

Al-Shifa head of surgery Marwan Abu Sada told AFP that Israeli troops were still in the hospital and it was surrounded by tanks.

"I heard at least two explosions since this morning," he said.

Doctors said Israeli troops were going from building to building and regularly detonated explosives on the ground floors and hospital basements searching for Hamas tunnels.

A Hamas health official said more than 80 people were killed on Saturday in twin strikes on Jabalia refugee camp, the territory's largest, including on a UN school sheltering displaced people.

The Israeli army said only that "an incident in the Jabalia region" was under review without elaborating.

"The horrendous events of the past 48 hours in Gaza beggar belief," United Nations High Commissioner for Human Rights Volker Turk said in a statement.

- Fuel shipments -

With just a trickle of aid allowed in from Egypt, Israel permitted a first consignment of fuel to enter Gaza late Friday under US pressure, allowing telecommunications to resume after a two-day blackout.

Some 120,000 litres (31,700 gallons) of fuel arrived on Saturday, according to the UN. 

Israeli Prime Minister Benjamin Netanyahu, whose government had vowed to keep aid out of Hamas's hands, said the fuel would power basic necessities like water pumps and sewage systems to prevent disease outbreaks.

A US official has said more fuel deliveries and a "significant pause" in fighting would come "when hostages are released".

Qatar's Prime Minister Mohammed bin Abdulrahman Al Thani said on Sunday a deal to free hostages hinges on "very minor" practical issues, without elaborating.

US deputy national security adviser Jon Finer told NBC they were "closer than we have been in quite some time" to securing a deal. But he added on CBS: "The mantra that nothing is agreed until everything is agreed really does apply."

Relatives of some of the hostages on Saturday marched to Netanyahu's Jerusalem office, demanding action to free them.

The bodies of two female captives were recovered in Gaza this week, the Israeli military said, while four abductees have so far been released by Hamas and a fifth rescued by troops.

US President Joe Biden threatened sanctions against Israeli settlers who have ramped up attacks on Palestinians in the West Bank in recent weeks.

Since the Israel-Hamas war began, Israeli troops and settlers have killed more than 200 Palestinians in the West Bank, according to the health ministry in Ramallah.

Also Sunday, the Iran-backed Huthi rebels claimed they had seized an Israeli ship in the vital waters of the Red Sea, but Israel denied the allegation.

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