Thousands of Palestinians sought refuge Saturday after Israel warned them to evacuate the northern Gaza Strip ahead of an expected ground offensive against Hamas, one week after the deadliest attack in Israel's history.

The Islamist group's militants gunned down, stabbed and burned more than 1,300 people in the attack Israel has compared to 9/11 in the United States, sparking a massive retaliatory bombing campaign targeting Hamas that has killed over 2,200 in Gaza.

Alarm has grown over the fate of Palestinian civilians in blockaded and besieged Gaza — one of the world's most densely populated areas, home to 2.4 million people — if it becomes the scene of intense urban combat and house-to-house fighting.

"The situation in Gaza has reached a dangerous new low," said UN Secretary-General Antonio Guterres. "Even wars have rules," he added, stressing that "civilians must be protected and also never used as shields".

Israel, which has vowed to destroy Hamas, has massed ground forces and tanks around Gaza, dropped leaflets in the north of the enclave telling civilians to flee, and staged "localized" raids "to cleanse the area of terrorists and weaponry", the army said.

The raids have also sought to locate "missing persons" inside Gaza, the military said, as Hamas has been holding some 150 hostages whose families have watched the escalating war with growing terror.

Israel has pounded Gaza targets with thousands of strikes in the past week, leaving at least 2,215 Gazans dead, including 724 children by Saturday, according to the health ministry in the Palestinian enclave.

"We wake up to the killing and death under the bombs," said Mohamed Abu Ali, a resident of the territory. "We don't know where to go, where is safe. We have no food, water or electricity."

In Geneva, the Red Cross said the unjustifiable "horrific" attacks on Israel could equally not justify "the limitless destruction of Gaza".

'Just the beginning'

Israel has been reeling from the bloodiest ever attack on the country and mourned the 1,300 victims it recovered in southern towns and kibbutz communities, which soldiers have cleared in battles that left 1,500 Hamas militants dead.

More than 100 people were killed in the community of Beeri alone, just outside Gaza, while around 270 mostly young people were shot dead or burned in their cars at the nearby Supernova music festival.

Prime Minister Benjamin Netanyahu warned that Israel's bombardment so far was "just the beginning" of the campaign to crush Hamas, a group which seeks the destruction of Israel and which he has likened to the Islamic State group.

In one strike, Israeli military "aircraft killed Ali Qadi, a company commander of the Hamas 'Nukhba' commando force" involved in the October 7 attack, a statement said Saturday.

Army spokesman Jonathan Conricus said on Saturday that Israeli forces were now "in formation… all around the Gaza Strip, in the south, in the center and in the north".

"We will likely evolve into additional significant combat operations," he said. "When we do so, remember how this started… All of this is Hamas-made."

With its evacuation order, Conricus said, Israel had "advertised our intentions in advance, not because it has any military logic — it doesn't — but because we want civilians not to be affected by the war… they are not our enemy."

He accused Hamas of using Gaza civilians as "their human shields".

Fears for hostages

Panic and fear reigned in the rubble-strewn streets of Gaza where hospitals have been overwhelmed with bloodied casualties and morgues have struggled to cope.

More than 1,300 buildings in Gaza have been destroyed, the UN said on Saturday, as more explosions rocked the ground and plumes of smoke billowed over Gaza City.

"What does the world want from us?" asked one Palestinian resident, Mohamed Khaled, 43. "I am a refugee in Gaza and they want to displace me yet again?"

A looming Gaza ground invasion has only heightened fears for the 150 hostages Hamas is holding and has threatened to kill in response to any unannounced Israeli strikes on civilian targets.

"I just want him back, to see him and to hug him," said Kanyarat Suriyasri, the wife of a Thai hostage taken by Hamas. "The rest is not important."

The militant group said Friday that 13 hostages had died in Israeli strikes, but offered no evidence.

US President Joe Biden spoke with the families of 14 Americans missing since the Hamas attack, telling CBS's "60 Minutes": "We're going to do everything in our power to find them."

Israel's army has confirmed contacting the families of 120 civilian hostages so far.

Egypt and Israel have meanwhile agreed to let US citizens leave the Gaza Strip through the Rafah crossing, said a US official accompanying Secretary of State Antony Blinken on a regional tour.

The official said the United States did not yet have confirmation that the agreement was being implemented, "but the intention was to have it open".

Wave of protests

The Hamas attack and the war it sparked — Gaza's fifth in 15 years — have upended Middle Eastern politics.

Tensions have risen with angry protests in support of the Palestinians held Friday in Bahrain, Iran, Iraq, Jordan, Lebanon and other many countries.

Palestinian prime minister Mohammad Shtayyeh accused Israel of committing "genocide" in Gaza, while clashes in the occupied West Bank have killed 53 Palestinians in the past week.

Netanyahu's spokeswoman Tal Heinrich told AFP: "Everything that happens in Gaza is Hamas's responsibility."

Palestinian president Mahmud Abbas said driving Gazans away will be "tantamount to a second Nakba" or "catastrophe", referring to the 760,000 Palestinians who fled or were expelled from their homes during the 1948 war that accompanied Israel's creation.

The United States has voiced strong support for Israel and sent military aid, while Blinken has been on a regional tour aiming to keep calm in the Arab world.

Israel faces the threat of a separate confrontation in the north, with the Iran-backed Hezbollah in Lebanon, after cross-border violence has repeatedly erupted for days.

A Reuters video journalist was killed and six other reporters — from AFP, Reuters and Al Jazeera — were wounded in southern Lebanon close to Israel, caught up in cross-border shelling.

Israeli forces said Saturday they had killed several "terrorists" trying to cross the border and also "struck a Hezbollah terror target in southern Lebanon" in response to a drone crossing the border.

'Forced transfer'

The Israeli military on Friday dropped flyers warning residents of northern Gaza to flee "immediately" to areas south of Wadi Gaza, with arrows pointing south on a map of the 40 kilometer-long (25 mile-long), 10 kilometre-wide territory.

There was confusion about the timeline for the mass evacuation order following reports of a 24-hour window.

EU foreign policy chief Josep Borrell said a plan to evacuate more than one million people in a single day was "utterly impossible to implement".

The Israeli military stressed on Saturday that Gaza City residents must not delay their departure before an offensive starts, as roads out of the northern part of the territory were again jammed with people leaving.

Military spokesman Richard Hecht said there is a "window" for safe passage to south Gaza between 10:00 am and 4:00 pm, without saying how many days the window would remain.

"We know this is going to take time but we recommend people not to delay," Hecht told reporters.

Thousands of Gazans have been on the move in search of safety, carrying plastic bags of belongings, suitcases on their shoulders and children in their arms.

Palestinians cannot leave the enclave blockaded by both Israel and Egypt, which has not opened its Rafah crossing with Gaza to refugees.

Arab League chief Ahmed Abul Gheit said Israel's order is a "forced transfer" that constitutes "a crime".

Concern for regional stability has prompted the United States to send additional munitions to Israel, and its largest aircraft carrier to the region.

Biden has issued stern warnings for other regional powers not to get involved.

Israel's arch foe Iran has long financially and militarily backed Hamas and praised its attack, but insists it was not involved.

In a sign of the regional upheaval, Saudi Arabia "has decided to pause discussion on possible normalization" of ties with Israel, a source familiar with the discussions told AFP.

Biden's administration had been pushing efforts for Saudi Arabia and Israel to establish diplomatic ties, following similar deals with a few other Arab states including the United Arab Emirates.