Joe Biden warned Benjamin Netanyahu that US support depends on “immediate action” from Israel, in his strongest hint yet that he is considering withholding arms sales.

In the first call between the two leaders since the deaths of the US-based World Central Kitchen group employees on Monday, Mr Biden also called for an “immediate ceasefire” after the “unacceptable” attack and wider humanitarian situation in Gaza.

Mr Biden is facing growing pressure in an election year over his support for Israel’s Gaza war with allies pressing him to consider making the billions of dollars in military aid sent by the United States to its key ally each year dependent on Netanyahu listening to calls for restraint.

The US president “made clear the need for Israel to announce and implement a series of specific, concrete, and measurable steps to address civilian harm, humanitarian suffering, and the safety of aid workers”, the White House said in a readout of the call.

“He made clear that US policy with respect to Gaza will be determined by our assessment of Israel’s immediate action on these steps.”

A key confidant of the president had earlier urged him to use the leverage afforded by the huge military aid that Washington gives Israel – something Mr Biden has resisted for the past six months.

“I think we’re at that point,” Chris Coons, a Democratic senator from the president’s home state of Delaware, told CNN.

If Israel began its long-threatened full-scale offensive in the southern city of Rafah, without plans for some 1.5 million people sheltering there, “I would vote to condition aid to Israel,” Mr Coons said.

“I’ve never said that before, I’ve never been there before,” he added.

Pressure from first lady

Mr Biden also reportedly faces pressure from even closer to home – from Jill Biden, the first lady.

“Stop it, stop it now,” she told the president about the growing toll of civilian casualties in Gaza, according to comments by Mr Biden himself to a guest during a meeting with members of the Muslim community at the White House, and reported by The New York Times.

Mr Biden has supported Israel’s six-month-old war sparked by Hamas’s October 7 attack, but has increasingly voiced frustration with Israel’s Right-wing prime minister over the soaring death toll and dire humanitarian situation in Gaza.

In his strongest statement since the war began, Mr Biden said Tuesday that he was “outraged and heartbroken” by Israel’s killing of the seven aid workers, who included a US-Canadian citizen. Israel has said the deaths were unintentional.

But Mr Biden’s words have not been matched by any concrete steps to limit the billions of dollars in military aid that Washington supplies to its bedrock regional ally.

In a sign of business as usual, Mr Biden’s administration approved the transfer of thousands more bombs to Israel on the same day as the Israeli strikes that killed the seven aid workers, The Washington Post reported on Thursday.

Many Democrats fear the controversy could hurt Mr Biden’s chances of reelection in November against Donald Trump, as Muslim and younger voters express their anger over Gaza.

A former senior aide to Barack Obama - the president under whom Mr Biden served as vice president - called for Mr Biden’s actions to back his words.

“The US government is still supplying two-thousand-pound bombs and ammunition to support Israel’s policy,” Ben Rhodes, a former deputy national security adviser in Obama’s administration, wrote on Twitter.

“Until there are substantive consequences, this outrage does nothing. Bibi (Netanyahu) obviously doesn’t care what the US says, it’s about what the US does.”

US voters are also increasingly turning against Israel’s Gaza offensive.

A majority of 55 per cent now disapprove of Israel’s actions, compared with 36 per cent who approve, according to a Gallup poll released on March 27.