(AFP) - The first aid trucks arrived in war-torn Gaza from Egypt on Saturday, bringing urgent humanitarian relief to the Hamas-controlled Palestinian enclave suffering what the UN chief labelled a "godawful nightmare".

Israel has vowed to destroy Hamas after the Islamist militant group carried out the deadliest attack in the country's history on October 7.

Hamas militants killed at least 1,400 people, mostly civilians who were shot, mutilated or burnt to death, and took more than 200 hostages, according to Israeli officials.

Israel has retaliated with a relentless bombing campaign on Gaza that has killed more than 4,300 Palestinians, mainly civilians, according to the Hamas-run health ministry.

An Israeli siege has cut food, water, electricity and fuel supplies to the densely populated and long-blockaded territory of 2.4 million people, sparking fears of a humanitarian catastrophe.

AFP journalists on Saturday saw 20 trucks from the Egyptian Red Crescent, which is responsible for delivering aid from various UN agencies, pass through the Rafah border crossing from Egypt into Gaza.

The crossing -- the only one into Gaza not controlled by Israel -- closed again after the trucks passed.

The lorries had been waiting for days on the Egyptian side after Israel agreed to a request from its main ally the United States to allow aid to enter.

UN chief Antonio Guterres warned Friday that the relief supplies were "the difference between life and death" for many Gazans, more than one million of whom have been displaced.

"Much more" aid needs to be sent, he told a peace summit in Egypt on Saturday.

US Secretary of State Antony Blinken welcomed the aid and urged "all parties" to keep the Rafah crossing open.

But a Hamas spokesman said "even dozens" of such convoys could not meet Gaza's needs, especially as no fuel was being allowed in to help distribute the supplies to those in need.

- 'Reeling in pain' -

Tens of thousands of Israeli troops have deployed to the Gaza border ahead of an expected ground offensive that officials have pledged will begin "soon".

As international tensions soar, Egyptian President Abdel Fattah al-Sisi was hosting a peace summit in Cairo on Saturday attended by regional and some Western leaders.

"The time has come for action to end this godawful nightmare," Guterres told the summit, calling for a "humanitarian ceasefire".

The region "is reeling in pain and one step from the precipice", he said.

Guterres said "the grievances of the Palestinian people are legitimate and long" after "56 years of occupation with no end in sight".

But he stressed that "nothing can justify the reprehensible assault by Hamas that terrorised Israeli civilians".

"Those abhorrent attacks can never justify the collective punishment of the Palestinian people," he added.

Egypt, historically a key mediator between Hamas and Israel, has urged "restraint" and the relaunch of the long-frozen peace process.

But diplomatic efforts to end the violence have made little headway, without the participation of Israel and its enemy Iran, a supporter of Hamas and other armed groups.

- 'Sliver of hope' -

A full-blown Israeli ground offensive carries many risks, including to the hostages Hamas took and whose fate is shrouded in uncertainty.

So the release of two Americans among the hostages -- mother and daughter Judith and Natalie Raanan -- offered a rare "sliver of hope", said Mirjana Spoljaric, president of the International Committee of the Red Cross.

US President Joe Biden thanked Qatar, which hosts Hamas's political bureau, for its mediation in securing the release.

He said he was working "around the clock" to win the return of other Americans being held.

Natalie Raanan's half-brother Ben told the BBC he felt an "overwhelming sense of joy" at the release after "the most horrible of ordeals".

Hamas said Egypt and Qatar had negotiated the release and that it was "working with all mediators to implement the movement's decision to close the civilian (hostage) file if appropriate security conditions allow".

Traumatised families with loved ones missing in Gaza demanded more action.

"We ask humanity to interfere and bring back all those young boys, young girls, mothers, babies," Assaf Shem Tov, whose nephew was abducted from a music festival where Hamas killed hundreds, said Friday.

- Devastation -

Almost half of Gaza's residents have been displaced, and at least 30 percent of all housing in the territory has been destroyed or damaged, the United Nations says.

Thousands have taken refuge in a camp set up in the city of Khan Yunis in southern Gaza.

Fadwa al-Najjar said she and her seven children walked for 10 hours to reach the camp, at some points breaking into a run as missiles struck around them.

"We saw bodies and limbs torn off and we just started praying, thinking we were going to die," she told AFP.

In Al-Zahra in central Gaza, Rami Abu Wazna was struggling to take in the destruction wreaked by Israeli missile strikes.

"Even in my worst nightmares, I never thought this could be possible," he said.

Israel's operation will take not "a day, nor a week, nor a month" and will result in "the end of Israel's responsibilities in the Gaza Strip", Defence Minister Yoav Gallant warned on Friday.

- Regional tensions flare -

In Gaza, retired general Omar Ashour said the destruction was "part of a clear plan for people to have no place left to live".

"This will cause a second Nakba," he added, referring to the 760,000 Palestinians who were expelled from or fled their homes when Israel was created in 1948.

The United States has moved two aircraft carriers into the eastern Mediterranean to deter Iran or Lebanon's Hezbollah, both Hamas allies, amid fears of a wider conflagration.

Fire across Israel's border with Lebanon continued overnight, with one Israeli soldier killed, Israeli public radio said. The military said it hit Hezbollah targets after rocket and missile fire.

Violence has also flared in the West Bank, where 84 Palestinians have been killed since October 7, according to the Palestinian health ministry.

© Agence France-Presse