The main UN aid agency in besieged Gaza warned it will have to stop operations by the end of Wednesday because it is running out of fuel, as Hamas said overnight Israeli strikes killed at least 80 people.

Alarm has grown about the spiralling humanitarian crisis in heavily bombarded Gaza where one doctor said he was forced to perform emergency surgery on the wounded without anaesthetic.

Israel has cut off impoverished Gaza's usual water, food and other supplies, and fewer than 70 relief trucks have entered since the war started -- "a drop of aid in an ocean of need", warned UN chief Antonio Guterres.

Israel launched withering strikes on Gaza in response to an unprecedented cross-border attack by Hamas militants who, while launching a massive rocket barrage, killed more than 1,400 people and took 222 hostages on October 7, according to Israeli authorities.

Prime Minister Benjamin Netanyahu has vowed to "eliminate Hamas" and Israeli bombing has now killed more than 5,800 people in Gaza, many of them children, according to the Hamas-run health ministry.

Inside the battered Palestinian territory, Abu Ali Zaarab, whose family house in Rafah was bombed, charged angrily that "they're not waging war on Hamas, they're waging war on children... It's a massacre."

Tempers flared at the United Nations where Guterres decried the "epic suffering" in Gaza and the "collective punishment" of its 2.4 million residents, drawing a furious response from Israel.

"Mr secretary-general, in what world do you live?" replied an infuriated Israeli Foreign Minister Eli Cohen, who recounted graphic accounts of civilians including young children killed in the deadliest single attack in Israeli history.

Israel's ambassador to the United Nations, Gilad Erdan, called on Guterres to resign, writing on X, formerly Twitter, that the UN chief had "expressed an understanding for terrorism and murder".

US President Joe Biden -- who has strongly backed Israel's war after what he called the "barbaric" Hamas attacks, but also brokered the entry relief trucks via Egypt -- shared the concern that the aid lifeline is "not fast enough".

US Secretary of State Antony Blinken said "food, water, medicine and other essential humanitarian assistance must be able to flow into Gaza" and that "humanitarian pauses must be considered for these purposes".

- 'This is a tragedy' -

On the 19th day of Israeli air and artillery strikes and a near-total land, sea and air blockade of Gaza, the UN agency for Palestinian refugees UNRWA warned operations are at breaking point.

"If we do not get fuel urgently, we will be forced to halt our operations in the Gaza Strip," said the agency which provides aid to 600,000 displaced in Gaza, where many families have slept in the open.

Israel has refused to allow fuel shipments into Gaza, fearing Hamas will use it for weapons and explosives and accusing the militant group of stockpiling supplies in large tanks.

Aid groups have warned that more people will die if medical equipment, water desalination plants and ambulances stop running in Gaza, where the only power plant went offline weeks ago.

Patients are already being treated on the floors of hospitals overwhelmed with thousands wounded by bombing. The Red Cross has warned that hospitals, once the generators stop running, "turn into morgues".

"We performed a number of surgeries on the wounded without anaesthetic," said Ahmad Abdul Hadi, an orthopaedic surgeon working in the emergency room of Nasser hospital, Khan Yunis.

"It's tough and painful, but with the lack of resources, what can we do?"

Aid agencies report that shelters and emergency tent cities are heaving under the weight of an estimated 1.4 million displaced -- more than half the population of the 40-kilometre (25-mile) long coastal strip.

Air strikes have kept hitting Gaza, where Israel says it is targeting Hamas sites, including tunnels and munitions depots, but where many residential buildings have been reduced to rubble.

Amine Abu Jazar, a displaced resident from Rafah, recounted how "at midnight, while we were sleeping, we suddenly felt shrapnel and rocks falling on us.

"We already have injured and martyrs among us, this is a tragedy. There's not even any electricity to see each other, the dead or the injured."

- Crisis diplomacy -

The Gaza war has sparked fears of a regional conflagration if it draws in more of Israels' enemies -- especially Iran-backed groups such as Lebanon's Hezbollah which has already traded deadly cross-border fire with Israel.

Israeli strikes also killed eight soldiers early Wednesday in the south of Syria, another Iran ally, state media reported, in what the Israeli army said was a response to earlier rocket fire.

Blinken told the UN Security Council that Washington "does not seek conflict with Iran" but also warned that "if Iran or its proxies attack US personnel anywhere, make no mistake, we will defend our people, we will defend our security -- swiftly and decisively".

Hezbollah leader met with Hamas and Palestinian Islamic Jihad senior representatives in Beirut Wednesday to discuss how "to achieve real victory... in Gaza and Palestine" and stop Israel's "brutal aggression", a statement said.

French President Emmanuel Macron -- the latest Western leader headed to the region for crisis diplomacy -- was in Jordan after visits to both Israel and the Palestinian territories and was later headed to Egypt.

Israel has meanwhile continued to mass tens of thousands of troops outside Gaza ahead of a ground offensive that has been anticipated for more than two weeks.

Military planners acknowledge it would mean difficult urban combat in a densely populated area latticed by tunnels and would imperil remaining civilians and the hostages.

"There are a lot of obstacles," an Israeli soldier serving with the military engineering corps told AFP on condition of anonymity.

"The enemy is spraying rockets and other things that I cannot detail to prevent us from progressing."

So far Hamas has released four hostages after mediation involving Qatar and Egypt, including Israeli Yocheved Lifshitz, 85, who later spoke of the "hell" of her abduction.

She recalled how gunmen raided her kibbutz home, threw her over the back of a motorbike and beat her as they raced back into Gaza, recounting that "they hurt me very much".

She and 79-year-old Nurit Cooper were released on "compelling humanitarian" grounds, according to Hamas, and Lifshitz also said the hostages were treated well once they were being held in captivity.

Both of their octogenarian husbands are still in Gaza along with more than 200 other Israeli and foreign hostages.

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