The main UN aid agency in the besieged Gaza Strip warned it will have to stop operations by the end of Wednesday because it is running out of fuel, as the territory's health ministry said Israeli strikes had killed 700 people in the past 24 hours.
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 ferocious and indiscriminate strikes on Gaza in response to an unprecedented cross-border attack by Hamas on October 7, killing 6,546 people as of Wednesday including 2,704 children.
More than 17,000 are also injured, with many critically injured.
Since the start of the war, Israel has also killed over 100 people in the West Bank, which it has illegally occupied since 1967 and where it has waged countless deadly military raids since March 2022.
Prime Minister Benjamin Netanyahu vowed to "eliminate Hamas" since the start of the war, but the vast majority of those killed in the strikes are civilians.
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 killed in Hamas's October 7 attack on Israel
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".
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, claiming 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, will "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 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."
The Gaza war has sparked fears of a regional conflagration if it draws in more of Israel's regional foes - especially Iran-backed groups such as Lebanon's Hezbollah, with whom Israel has already traded deadly cross-border fire.
At least 49 people have been killed in Lebanon, including 46 mostly Lebanese and Palestinian fighters.
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 occupied Palestinian territories and was later headed to Egypt.