The UN said the mass relocation of the entire population in northern Gaza to the south of the enclave was "impossible" and urgently appealed for the order to be rescinded.

The UN said it had been informed of the order shortly before midnight Thursday, six days after Hamas gunmen killed more than 1,200 people in Israel and took about 150 hostages in the deadliest attack since the country's creation in 1948.

Israel has retaliated by raining air and artillery strikes in Gaza for six days, claiming more than 1,400 lives and displacing over 400,000 people in the crowded enclave.

It is preparing for a possible ground invasion of the Palestinian territory after what has been labelled Israel's 9/11. 

The Israeli army confirmed Friday it had called on Gaza City residents to evacuate to the south.

UN officials working in Gaza said earlier they were informed by the Israeli military "that the entire population of Gaza north of Wadi Gaza should relocate to southern Gaza within the next 24 hours". 

Stephane Dujarric, spokesman for the UN secretary-general told AFP, that amounted  to around 1.1 million people, adding that the order also applied to all UN staff and those sheltered in UN facilities –- including schools, health centres and clinics.

"The United Nations strongly appeals for any such order, if confirmed, to be rescinded avoiding what could transform what is already a tragedy into a calamitous situation," Dujarric said, before Israel's confirmation.

The Israel's Ambassador to the UN, Gilad Erdan, reacted angrily to the UN saying its response to the warning to Gaza residents as "shameful!"

"For many years, the UN has turned a blind eye to the arming of Hamas and its use of the civilian population and civilian infrastructure in the Gaza Strip as a hiding place for its weapons and murder," Erdan said in a note from his office to AFP. 

Safe passage? 

There are 2.4 million people living in Gaza who are now enduring the fifth war in 15 years in the coastal enclave.

Israeli fighter jets and drones have flown above Gaza in a relentless bombardment that has levelled entire blocks and destroyed thousands of buildings.

More than 423,000 people have already fled their homes in Gaza, according to the UN.

Cairo faced calls to allow safe passage for fleeing civilians, but Egypt's President Abdel Fattah al-Sisi on Thursday urged Gazans to "stay steadfast and remain on their land".

Israel has cut off water, food and power supplies to Gaza in a siege it has vowed will not end until all hostages are freed.

"Humanitarian aid to Gaza? No electric switch will be turned on, no water tap will be opened and no fuel truck will enter until the Israeli abductees are returned home," Israeli Energy Minister Israel Katz said.

Hamas has threatened to kill hostages if Israel bombs Gaza civilian targets without advance warning.

"I know he's out there somewhere," one of the affected Israelis, Ausa Meir, said of her brother Michael, who is among the captives. 

"It's very, very painful."

US support 

The United States has vowed unwavering support for Israel in its war on Hamas.

"You may be strong enough on your own to defend yourself," US Secretary of State Antony Blinken said at a joint press conference in Tel Aviv with Prime Minster Benjamin Netanyahu on Thursday.

"But as long as America exists, you will never, ever have to. We will always be there by your side." 

Netanyahu voiced appreciation for the US support, which includes military aid, and said Hamas, which rules the blockaded Gaza Strip, should be treated like the Islamic State group.

"Just as ISIS was crushed, so too will Hamas be crushed. And Hamas should be treated exactly the way ISIS was treated," Netanyahu said. 

Blinken meanwhile stressed that Hamas did not represent the Palestinian people.

"Anyone who wants peace and justice must condemn Hamas's reign of terror," Blinken said.

Blinken then travelled to Jordan, where he will meet King Abdullah II and Palestinian leader Mahmud Abbas on Friday.

He will also go to Saudi Arabia, Egypt, the UAE and Qatar to put pressure on Hamas and secure the release of hostages. 

Hospital morgues 

The International Committee of the Red Cross Middle East chief Fabrizio Carboni warned Gaza's hospitals "risk turning into morgues".

At the biggest, al-Shifa Hospital, there were chaotic scenes Thursday of an uninterrupted stream of ambulances, relatives asking for news and wails of anguish from relatives of the dead.

An AFP team saw dozens of bodies wrapped in white shrouds in cold storage units and covering the floor of the mortuary.

In his first public remarks since Hamas attacked Israel, Palestinian president Abbas called for an "immediate end to comprehensive aggression against the Palestinian people".

The UN humanitarian agency has launched an urgent appeal for nearly $300 million to address the most urgent needs in Gaza and the occupied West Bank.

'Depravity' 

Netanyahu's account on X, formerly Twitter, said he showed Blinken "photos of babies murdered and burned by the Hamas monsters". 

Blinken told reporters later the images were "new evidence of depravity and the inhumanity of Hamas". 

But Hamas denied its fighters killed infants during the assault on Saturday.  

Political bureau member Ezzat al-Rishaq called it a "fake and false Israeli narrative", insisting "no evidence has been submitted to support such false claims".

Military build-up 

Israel has called up 300,000 reservists and rushed forces, tanks and heavy armour to the southern desert areas around Gaza from where Hamas fighters launched their unprecedented attack on October 7.

Israeli soldiers have since then swept the southern towns and kibbutz communities and killed 1,500 of the militants, while making ever more shocking discoveries of large numbers of dead civilians.

"It looks like ... an atomic bomb just landed here," Doron Spielman, an Israeli army spokesman, said at one gated community where more than 100 residents were killed.

Hezbollah threat 

Israel's war now flaring in the south is further complicated by a threat from the north, the Iran-backed Hezbollah group based in Lebanon.

The army has massed tanks on the border after repeated clashes with Hezbollah in recent days, including cross-border rockets and shelling.

The United States has sent munitions to Israel and deployed an aircraft carrier battle group to the eastern Mediterranean in a show of support, while warning Israel's other enemies not to enter the conflict.

In London, the UK said it was sending two Royal Navy ships and surveillance aircraft to the eastern Mediterranean to support Israel, as well as "ensure regional stability and prevent further escalation".

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

Iran's ultra-conservative President Ebrahim Raisi called on Islamic and Arab countries to confront Israel and support the "oppressed Palestinian nation", in a phone call with his Syrian ally Bashar al-Assad.

Israel also struck Syria's two main airports, in Damascus and Aleppo, in "simultaneous" attacks on landing strips that put them out of service", state media said, citing an unidentified military source.