PALESTINIAN TERRITORIES - Gaza's Hamas rulers warned on Saturday that Israel's planned army operation in overcrowded Rafah could cause "tens of thousands" of casualties in the city, the last refuge for displaced Palestinians.

Israeli Prime Minister Benjamin Netanyahu has ordered the army to set its sights on Rafah. He told military and security officials late Friday to "submit to the cabinet a combined plan for evacuating the population and destroying the battalions" of Hamas in the southern city.

Hamas said in a statement that any military action would have catastrophic repercussion that "may lead to tens of thousands of martyrs and injured if Rafah... is invaded".

Netanyahu's announcement, coming after US President Joe Biden had issued his strongest criticism of Israel's response to the October 7 attack, sparked concern among world leaders and the United Nations.

"The Israeli occupation's move threatens security and peace in the region and the world. This is a blatant violation of all red lines," said the office of Palestinian president Mahmud Abbas.

The EU's foreign policy chief Josep Borell posted on X, formerly Twitter, Saturday: "I echo the warning by several EU member states that an Israeli offensive on Rafah would lead to an unspeakable humanitarian catastrophe and grave tensions with Egypt.

"Resuming negotiations to free hostages and suspend hostilities is the only way to avert a bloodshed."

Jordan's Foreign Minister Ayman Safadi warned "another bloodbath in Gaza cannot be allowed", in a post on X.

British Foreign Secretary David Cameron said he was "deeply concerned about the prospect of a military offensive in Rafah.

"The priority must be an immediate pause in the fighting to get aid in and hostages out," he posted.

- Biden frustration -

The war in Gaza was sparked by Palestinian Islamist group Hamas's unprecedented October 7 attack on Israel, which resulted in the deaths of about 1,160 people, mostly civilians, according to an AFP tally based on official figures.

Vowing to eliminate Hamas, Israel launched a massive military offensive in Gaza that the territory's health ministry says has killed at least 28,064 people, mostly women and children.

Militants seized 250 hostages, 132 of whom are still in Gaza although 29 are presumed dead, Israel has said.

The United States is Israel's main international backer, providing it with billions of dollars in military aid.

The US State Department has said it does not support a ground offensive in Rafah, warning that, if not properly planned, such an operation risks "disaster".

In a sign of growing frustration, Biden issued his strongest criticism of Israel yet on Thursday, describing the retaliation for Hamas's October 7 attack as "over the top".

Biden said there are "a lot of innocent people who are starving... in trouble and dying, and it's got to stop."

But Netanyahu's office said it would be "impossible" to achieve the war's objective of eliminating Hamas while leaving four of its battalions in Rafah.

- Pressure on UNRWA chief -

The Israeli military said it had killed two "senior Hamas operatives" in an air strike on Rafah Saturday.

It was part of a wider bombardment that killed at least 25 people in the city, according to the health ministry.

Israel's military claimed that troops had uncovered a Hamas tunnel under the evacuated Gaza City headquarters of the UN agency for Palestinian refugees (UNRWA).

Israeli Foreign Minister Israel Katz called for its head, Philippe Lazzarini, to quit.

Lazzarini said the agency had not operated from the compound since October 12 when staff evacuated it under instruction from Israeli forces.

Already under pressure after Israel claimed 12 UNRWA staff were involved in the October 7 Hamas attack, he called for an independent investigation into the latest Israeli accusations.

An AFP photographer was among a number of journalists taken to the compound and tunnel by the Israeli military on Thursday.

UN premises are considered "inviolable" in international law and immune from "search, requisition, confiscation, expropriation and any other form of interference".

Hamas has repeatedly denied Israeli accusations that it has dug a network of tunnels under schools, hospitals and other civilian infrastructure as cover for its activities.

- 'Between life and death' -

Fears are mounting over the fate of more than one million displaced Palestinians who have taken shelter in Rafah, many of them in plastic tents pushed up against the border with Egypt.

"We are between life and death," said one of them, Bassel Matar. "We don't know if there will be hope tomorrow for a truce or there will be changes on the ground."

Rafah is the last major population centre in the Gaza Strip that Israeli troops have yet to enter and also the main point of entry for desperately needed relief supplies.

Humanitarian organisations have expressed alarm at the prospect of a ground incursion.

The UN children's fund, UNICEF, warned this week that "thousands more could die in the violence or lack of essential services".

Netanyahu announced the plan for a ground operation in Rafah only days after US Secretary of State Antony Blinken visited Israel seeking a ceasefire and hostage-prisoner exchange.

The impact of the war has been felt widely, with violence involving Iran-backed allies of Hamas surging across the Middle East.

A senior Hamas officer survived an Israeli assassination attempt in Lebanon, Palestinian and Lebanese security sources told AFP, but two other people including a Hezbollah member were killed in the attack.

And in Syria, Israeli strikes near Damascus killed three people, a war monitor said, adding the targeted neighbourhood hosted villas for top military and civilian officials.