More than 100 trucks carrying aid goods have been queued for days on the Egyptian side of the Rafah border crossing.
Palestinians in war-torn Gaza on Thursday eagerly awaited aid trucks promised in a deal struck by US President Joe Biden with Egypt and Israel, as the army struck more Hamas targets.
The war -- sparked by the bloody October 7 Hamas attack on Israel that officials said has claimed more than 1,400 lives -- has set off fury across the Middle East against Israel and its Western allies.
The conflict has claimed at least 3,785 lives in the Gaza Strip, its Hamas-controlled health ministry said Thursday, with entire city blocks levelled, water, food and power cut off, and more than one million displaced.
"The pace of death, of suffering, of destruction... cannot be exaggerated," UN humanitarian chief Martin Griffiths said about the situation in the crowded territory of 2.4 million people.
There are fears of worse to come if Israel launches an anticipated ground invasion to destroy Hamas and rescue Israeli and foreign hostages, whose known number Israel on Thursday revised up to 203.
Biden, on a flying visit to meet Prime Minister Benjamin Netanyahu and his war cabinet on Wednesday, reiterated strong US support for its long-time ally but also stressed the need to address the plight of Palestinian civilians.
He said he had agreed a deal for an initial 20 trucks carrying relief goods to pass through the shuttered Rafah crossing from Egypt into Gaza, with the first deliveries expected Friday at the earliest.
"We want to get as many of the trucks out as possible," Biden told reporters on Air Force One as he flew home, while warning that "if Hamas confiscates it or doesn't let it get through... then it's going to end".
Amid the flaring crisis, UN Secretary-General Antonio Guterres headed to Egypt on Thursday, where President Abdel Fattah al-Sisi also hosted Jordan's King Abdullah II.
The pair, whose countries were the first Arab states to normalise relations with Israel in 1979 and 1994, condemned the "collective punishment" of Gazans and warned about the conflict spreading.
"If the war does not stop", it threatens "to plunge the entire region into catastrophe", a statement from the Jordanian royal court read.
Sisi and Abdullah -- seen as key mediators between Israel and the Palestinians -- had been due to have four-way talks with Palestinian president Mahmud Abbas and Biden.
But Amman cancelled the summit.
More than 100 trucks carrying aid goods have been queued for days on the Egyptian side of the Rafah border crossing, the only entry or exit point to Gaza not controlled by Israel.
Cairo has so far kept it closed, pointing to repeated Israeli strikes near the checkpoint and voicing fears that Israel may be hoping to permanently drive Palestinians out and into Egypt's Sinai desert.
On the Gaza side, scores of people were again waiting, desperate to flee, but careful to keep about 100 metres (300 feet) away in case of new Israeli bombardment.
"We're ready with our bags," said one man who only gave his name as Mohammed, 40, and who said he works for a European institution.
He said he had been waiting "for three days with my family, in a house 10 minutes away from the crossing" but had received no information so far.
Majed, 43, who said he works with a German organisation, told AFP: "I came on my own this morning and, in case the crossing opens, I'd get my wife and children -- they're ready."
Biden, who was due to address the nation on Thursday about the Gaza and Ukraine conflicts, announced the aid truck deal after what he called "blunt" talks in Israel and a phone call with Egyptian President Abdel Fattah al-Sisi.
Israel consented to the deal while pressing on with its military campaign.
Its army reported Thursday that it had destroyed hundreds more Hamas targets, including missile launch site and tunnels, and that "more than 10 terrorists were eliminated".
Israel has stressed it must destroy Hamas after the worst attack on its soil which, the army said Thursday, had claimed 1,403 lives since the surprise onslaught on October 7 including at least 306 soldiers killed in battles to reclaim overrun villages and kibbutzim.
Biden, the first US president to visit Israel during war time, strongly backed Israel but warned it not to overreact, cautioning that Washington made mistakes as it sought to avenge 9/11.
UK Prime Minister Rishi Sunak on Thursday became the latest foreign leader to make a solidarity visit to Israel, meeting Netanyahu and President Isaac Hertzog.
He backed Israeli action but also stressed the need for getting aid into Gaza, before jetting to Saudi Arabia for talks with Crown Prince Mohammed bin Salman.
Netanyahu called Israel's fight-back a "just war", adding: "I've never seen the people of Israel as united -- more united -- than they are now," he said.
But intensifying cross-border fire between Israel and the Iran-backed Hezbollah movement in Lebanon is stoking fears of a potential second front.
As tensions mounted, the United States and UK on Thursday advised their citizens to leave Lebanon while flights were still available.
The Arab world has been united in anger and condemnation of Israel since a deadly strike hit a Gaza hospital compound on Tuesday.
Both sides in the war have traded blame for the bloody carnage, but neither the provenance of the strike nor the death toll could be immediately or independently verified.
The strike left scores of bodies and charred cars at the Ahli Arab hospital compound in northern Gaza, AFP images showed.
Hamas accused Israel of hitting the hospital during its massive bombing campaign and Gaza's health ministry put the death toll at 471.
Israel blamed a misfired Islamic Jihad rocket, a claim backed by Biden who said the US Defense Department had concluded that "it's highly unlikely that it was the Israelis. It would have had a different footprint".
The Israeli military has pointed to the absence of a large impact crater typical of its air strikes and said fuel from the errant rocket had exploded.
A senior European intelligence source told AFP that he believed a maximum of 50 people were killed.
Israeli army spokesman Jonathan Conricus has also disputed Hamas's figure of 471 dead, asking "where are all the bodies?"
Hamas has dismissed Israel's position, saying its "outrageous lies do not deceive anyone".
It also slammed the United States, accusing it of being complicit in the ongoing strikes on Gaza.