The leaders of the United States and Israel were set to speak on Thursday after Washington expressed "outrage" over Israel's killing of seven aid workers and growing concern over its military operations in besieged Gaza.

President Joe Biden and Prime Minister Benjamin Netanyahu will hold their first phone discussions since the Israeli strikes killed the employees of the US-based charity World Central Kitchen on Monday.

The bodies of six foreign staff of WCK -- Australian, British, Polish and US-Canadian citizens -- were repatriated from Gaza via Egypt on Wednesday, while the Palestinian employee was laid to rest in Gaza.

Biden said he was "outraged and heartbroken" by the attack which drew condemnation worldwide including from the UN secretary-general and the pope.

Biden and Netanyahu were also expected to discuss Israel's plans to send ground forces into Gaza's densely crowded southern city of Rafah, and Israel's wider conflict with Iran and its allies after it was blamed for a deadly strike on the Iranian consulate building in Damascus.

Pentagon chief Lloyd Austin too expressed "outrage" at the aid workers' killings -- which Israel has admitted to -- in a phone call with his Israeli counterpart Yoav Gallant.

Austin stressed the need to protect aid workers and civilians and for "a rapid increase of aid" into Gaza, "particularly to communities in northern Gaza that are at risk of famine," the Pentagon said.

He said the aid charity "tragedy reinforced the expressed concern over a potential Israeli military operation in Rafah, specifically focusing on the need to ensure the evacuation of Palestinian civilians and the flow of humanitarian aid".

The Israeli army said Gallant and Austin had discussed "plans to expand operations to address Hamas's remaining battalions and military capabilities".

It said the two had also "discussed the threat posed by Iran and its proxy activities", after Israel was blamed for the Damascus strike Monday that killed seven Iranian Revolutionary Guards, two of them generals.

Iran's supreme leader Ayatollah Ali Khamenei vowed in a social media message that "with God's help we will make the Zionists repent of their crime of aggression against the Iranian consulate in Damascus".

The Israeli military said that, after a "situational assessment, it was decided to increase manpower and draft reserve soldiers".

The army also said "leave will be temporarily paused for all combat units", and media reported that more reservists were being called up "against the background of the visible threats from Iran".

As Netanyahu has fought the war, he has faced intense domestic pressure from the families and supporters of the hostages still held in Gaza, and from a resurgent anti-government protest movement.

A street protest in Tel Aviv to highlight the hostage crisis featured signs that warned "they are out of time", and a gagged man whose hands were tied with wire.

War cabinet member Benny Gantz, a centrist political rival of Netanyahu, has demanded that a snap election be held in September, a call rejected by the premier's right-wing Likud party.

Talks for a ceasefire and hostage release deal have stalled. An informed source within Hamas told AFP that "there is nothing new in the latest negotiating round, and the occupation (Israel) continues to be stubborn, procrastinate and disrupt any ceasefire agreement".

Amid the heightened tensions, Israeli security services said they had foiled a plot to kill the far-right National Security Minister Itamar Ben Gvir, who heads the Jewish Power party, and to strike other targets.

 'Food for our families'

In war-torn Gaza, where vast areas have been reduced to rubble, 2.4 million Palestinians have struggled on under bombardment while enduring dire shortages of food, water, fuel and other basic supplies.

The charity Oxfam said that people in northern Gaza have been forced to survive on an average of 245 calories a day -- less than a can of beans, and a fraction of the recommended average daily 2,100 calorie intake per person.

In Gaza City, Palestinians spent the night near an aid delivery spot, hoping to secure a bag of flour.

"We sleep on the streets, in the cold, on the sand, enduring hardship to secure food for our families, especially our young children," one man told AFP. "I don't know what else to do or how our lives have come to this."

WCK, which has called Monday's Israeli strikes "targeted", suspended its Gaza operations and sent ships laden with undelivered supplies back to Cyprus.

The International Committee of the Red Cross warned that "humanitarian aid organisations are unable to carry out their work safely".