Heavy fighting rocked besieged Gaza on Wednesday as aid agencies warned of looming famine, a day after a UN Security Council resolution calling for an immediate ceasefire was blocked by a US veto.

Washington, which argued the resolution would have imperilled ongoing efforts to free hostages, sent top White House official Brett McGurk to Cairo for renewed talks involving mediators and Hamas.

Global concern has spiralled over the high civilian death toll and dire humanitarian crisis in the war sparked by Hamas's October 7 attack against Israel.

Combat and chaos again stalled the sporadic aid deliveries for desperate civilians in Gaza, where the UN has warned the population of 2.4 million is on the brink of famine and could face an "explosion" of child deaths.

The UN World Food Programme said it was forced to halt aid deliveries in north Gaza because of "complete chaos and violence" after a truck convoy encountered gunfire and was ransacked by looters.

More Israeli strikes pounded Gaza, leaving 103 people dead during the night, according to the health ministry in the Hamas-run territory, which put the overall death toll at 29,313.

"We can't take it anymore," said Ahmad, a resident of Gaza City, where entire blocks are in ruins and cratered streets are strewn with rubble.

"We do not have flour, we don't even know where to go in this cold weather," he said. "We demand a ceasefire. We want to live."

Particular concern has centred on Gaza's far-southern Rafah area, where 1.4 million people now live in crowded shelters and makeshift tents, fearing attack by nearby Israeli ground troops.

Aid groups warn a ground offensive could turn Rafah into a "graveyard" and the United States has said the vast numbers of displaced civilians must first be moved out of harm's way.

US National Security Council spokesman John Kirby said that "without properly accounting for the safety and security of those refugees, we continue to believe that an operation in Rafah would be a disaster".

Israeli Prime Minister Benjamin Netanyahu has insisted the army will keep fighting until it has destroyed Hamas and freed the remaining 130 hostages, around 30 of whom are feared dead.

War cabinet minister Benny Gantz has warned that, unless Hamas releases the captives by the start of Ramadan around March 10, the army will keep fighting during the Muslim holy month, including in Rafah.

- 'More massacres' -

The war started when Hamas launched its unprecedented attack on October 7, which resulted in the deaths of about 1,160 people in Israel, mostly civilians, according to an AFP tally of Israeli figures.

Hamas also took about 250 hostages, many of whom were released during a week-long truce in late November.

Israel has heavily bombed Gaza and launched a ground invasion that has seen troops and tanks push through from the north towards the south, leaving vast swathes entirely destroyed.

The World Health Organization called the devastation "indescribable" around Nasser Hospital in the southern city of Khan Yunis, where it said it managed to evacuate some 32 patients.

"The area was surrounded by burnt and destroyed buildings, heavy layers of debris, with no stretch of intact road," WHO said.

The clinic has no power or running water, it added, and "medical waste and garbage are creating a breeding ground for disease".

Major powers have tried to navigate a way out of the crisis, so far without success.

On Tuesday the UN Security Council voted on an Algeria-drafted resolution which demanded an immediate humanitarian ceasefire and the release of all hostages.

The United States vetoed the resolution, which it labelled "wishful and irresponsible", drawing strong criticism from China, Russia, Saudi Arabia and even close ally France.

Hamas said the US veto amounted to "a green light for the occupation to commit more massacres".

- US envoy in Cairo -

Washington sent McGurk, the White House coordinator for the Middle East and North Africa, to Egypt as part of efforts to advance a hostage deal, before he heads to Israel Thursday.

Hamas chief Ismail Haniyeh was already in Cairo for talks, the militant group said -- days after mediators warned that prospects for a truce had dimmed despite repeated talks.

Qatar and Egypt have proposed a plan to free hostages in return for a pause in fighting and the release of Palestinian prisoners, but Israel and Hamas have so far failed to agree on a deal.

McGurk will hold talks "to see if we can't get this hostage deal in place," Kirby told reporters.

As the bloodiest ever Gaza war has continued into a fifth month, Israel has faced a growing international chorus of criticism.

Colombian President Gustavo Petro accused Israel of "genocide" after Brazilian President Luiz Inacio Lula da Silva had compared the Gaza campaign to the Holocaust.

The war has set off clashes elsewhere in the Middle East, drawing in Iran-backed armed groups in Lebanon, Syria, Iraq and Yemen.

Israel has traded almost daily cross-border fire with Lebanon's Hezbollah, and US and British forces have hit Yemen's Huthi rebels to deter their attacks on shipping in the Red Sea.

In Syria, state television said an Israeli missile strike killed at least two people in Damascus, a claim Israel declined to comment on.

Violence has also flared in the occupied West Bank where the Israeli army said its troops killed three Palestinian militants during an overnight raid in the northern city of Jenin.