The United Nations has said it is “impossible” for Palestinians to move to the south of Gaza in the next 24 hours, after citizens were ordered to evacuate by Israel’s military.

It came as the UN’s Palestinian refugee agency warned Gaza was becoming a “hell hole” and was on the “brink of collapse”.

The evacuation order is the strongest hint yet from Israel that it is preparing to launch a ground offensive on Gaza almost a week after Hamas’s surprise assault.

It also began dropping leaflets written in Arabic into the Gaza Strip urging people in the north of the area to move south across the Wadi Gaza – a piece of coastal wetland with a river running through the middle.

UN officials in Gaza “were informed by their liaison officers in the Israeli military that the entire population of Gaza north of Wadi Gaza should relocate to southern Gaza within the next 24 hours,” UN spokesman Stephane Dujarric said in a statement in New York.

“This amounts to approximately 1.1 million people,” he added, or nearly half of Gaza’s 2.3 million population.

Mr Dujarric said the UN “considers it impossible for such a movement to take place without devastating humanitarian consequences”.

It came after the Israel Defence Forces (IDF) said “this evacuation is for your own safety”, but in response, Hamas has called the warning “fake propaganda” and urged Palestinians “not to fall for it”.

The UN has appealed for the order to be rescinded to avoid turning “what is already a tragedy into a calamitous situation”.

Israel ‘strikes Syrian airports’ – follow live conflict updates

Palestinian President Mahmoud Abbas told US Secretary of State Antony Blinken in Amman on Friday that he “rejects the forced displacement” of Palestinians in Gaza, the official Palestinian news agency WAFA reported.

He said such an event would constitute a “second Nakba” – referring to the mass displacement of Palestinians in the 1948 war surrounding Israel’s creation – adding that humanitarian corridors must be allowed in the blockaded coastal enclave immediately to prevent a humanitarian disaster.

The Palestine Red Crescent Society (PRCS) called for an “immediate intervention” from the international community to prevent a “humanitarian catastrophe”.

“We don’t have the means to evacuate the sick and the wounded people in our hospitals or the elderly and the disabled,” a spokesperson for the humanitarian group said.

The World Health Organisation (WHO) said local health authorities in Gaza had informed its officials it was impossible to evacuate vulnerable hospital patients from northern Gaza within 24 hours.

“There are severely ill people whose injuries mean their only chances of survival is being on life support, such as mechanical ventilators,” said WHO spokesperson Tarik Jasarevic.

“So moving those people is a death sentence. Asking health workers to do so is beyond cruel.”

In other key developments:
• It’s “highly likely” Britons are among Hamas’s hostages, Defence Secretary Grant Shapps says
• Hamas claimed Israel killed 13 hostages with its strikes on Gaza
• Humza Yousaf’s mother-in-law shared a tearful plea from Gaza
• UK navy to send ships and begin surveillance flights over Israel
• Several UK Jewish schools close for safety reasons

Sunak shows support as number of dead grows

Earlier, Rishi Sunak told Israel’s prime minister to “protect ordinary Palestinians” as it continues its fightback against Hamas.

A Number 10 spokeswoman said Mr Sunak “reiterated that the UK stands side by side with Israel in fighting terror” in his phone call with Benjamin Netanyahu, adding Hamas should “never again be able to perpetrate atrocities against the Israeli people”.

Read more on this story:
Why Israel is braced for Hezbollah attack from Lebanon
How negotiators will be working to free Hamas hostages

Israel said a total of 1,300 of its people have died since Saturday’s raids as its troops continue to mass along the barbed wire fence ahead of a possible ground offensive on Gaza, with 300,000 reservists called up.

The country is targeting Hamas after the militant group carried out a wave of attacks in Israel as gunmen stormed the border and killed hundreds in their homes – as well as 260 others at a music festival.

Meanwhile, at least 500 children and 276 women are among the estimated 1,537 Palestinians who have died with more than 6,000 wounded, the Gaza health ministry has said.

White phosphorous used, human rights group claims

On the ground in Gaza, it has been claimed white phosphorous has been used as a weapon, which can indiscriminately burn people, thermally and chemically.

Human Rights Watch said Israel used the chemical in Gaza and Lebanon, claiming it had verified footage from 10 and 11 October, respectively, showing multiple airbursts of artillery-fired white phosphorus over the Gaza City port and two rural locations along the Israel-Lebanon border.

It said the weapon’s use “violates the international humanitarian law prohibition on putting civilians at unnecessary risk”.

Asked for comment on the allegations, Israel’s military said it was “currently not aware of the use of weapons containing white phosphorous in Gaza”.

Elsewhere on Friday, tens of thousands of people gathered in Tahrir Square in Iraq’s capital of Baghdad to show solidarity with Palestine.

Protesters also took to the streets of Iran – a key backer of Hamas – in support of the Palestinian people.

Jordan’s King Abdullah on Friday responded to Israel’s evacuation order, and warned its neighbour against any attempt to forcibly displace Palestinians.

In a statement published by the Royal Court, he said there should be no “spillover” of the ongoing crisis into neighbouring countries.

Jordan, which borders Israel to the southeast, maintains peaceful – though often tense – relations with the Israeli government.