Three British aid workers killed by an Israeli air strike in Gaza have been hailed as “heroes” amid mounting international condemnation of the attack.

World Central Kitchen (WCK) confirmed British victims John Chapman, 57, James “Jim” Henderson, 33, and James Kirby, 47, who were working for the charity’s security team, were among seven of its staff killed.

The team’s leader, Lalzawmi “Zomi” Frankcom, 43, an Australian national, also died, along with American-Canadian dual citizen Jacob Flickinger, 33, Polish national Damian Sobol, 35, and Palestinian Saifeddin Issam Ayad Abutaha, 25.

According to The Times, Mr Henderson was a former Royal Marine from Cornwall who was due to leave Gaza on Monday.

Mr Chapman, a father-of-two from Poole, Dorset, was also said to be a former Royal Marine and served in the Special Boat Service, the special forces unit of the Royal Navy, according to The Sun.

Mr Kirby is also believed to be a military veteran and a former member of Britain’s special forces.

The Telegraph reported he was a former Army rifleman and sniper marksman.

WCK’s chief executive Erin Gore described the victims as “the heroes of World Central Kitchen”.

US President Joe Biden said he was “outraged and heartbroken” by the deaths and said he had spoken to WCK founder Jose Andres.

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James ‘Jim’ Henderson was one of seven World Central Kitchen aid workers who were killed in the Israeli air strike in Gaza (World Central Kitchen/PA)

“This is not a standalone incident,” he said. “This conflict has been one of the worst in recent memory in terms of how many aid workers have been killed.

“This is a major reason why distributing humanitarian aid in Gaza has been so difficult – because Israel has not done enough to protect aid workers trying to deliver desperately needed help to civilians.

“Incidents like yesterday’s simply should not happen.”

He said an Israeli investigation “must be swift, it must bring accountability and its findings must be made public”.

“I will continue to press Israel to do more to facilitate that aid,” he said. “And we are pushing hard for an immediate ceasefire as part of a hostage deal. I have a team in Cairo working on this right now.”

The convoy was hit as it was leaving the Deir al-Balah warehouse, where the team had unloaded more than 100 tonnes of humanitarian food aid taken to Gaza on the maritime route, the charity said.

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Former Royal Marine John Chapman had been due to leave Gaza on Monday (World Central Kitchen/PA)

WCK immediately suspended operations in the region.

Israeli Prime Minister Benjamin Netanyahu confirmed Israeli forces were behind the “unintended strike” on Tuesday.

During a phone call with Mr Netanyahu, Rishi Sunak said he was appalled by the killings and demanded a thorough and transparent independent investigation.

A Downing Street spokesman said: “The Prime Minister spoke to Israel’s prime minister, Benjamin Netanyahu, this evening.

“He said he was appalled by the killing of aid workers, including three British nationals, in an air strike in Gaza yesterday and demanded a thorough and transparent independent investigation into what happened.

“The Prime Minister said far too many aid workers and ordinary civilians have lost their lives in Gaza and the situation is increasingly intolerable.

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Former military veteran James Kirby had been working for World Central Kitchen’s security team (World Central Kitchen/PA)

“The UK expects to see immediate action by Israel to end restrictions on humanitarian aid, deconflict with the UN and aid agencies, protect civilians and repair vital infrastructure like hospitals and water networks.

“The Prime Minister reiterated that Israel’s rightful aim of defeating Hamas would not be achieved by allowing a humanitarian catastrophe in Gaza.”

Lt Gen Herzi Halevi, chief of the general staff of the Israel Defence Forces, said the incident was “a mistake that followed a misidentification – at night during a war in very complex conditions. It shouldn’t have happened”.

He added that an independent body would conduct a “thorough investigation” which is to be completed in the coming days.

Foreign Secretary David Cameron said the killings were “completely unacceptable” as he pressed Israel for “major changes” to ensure the safety of aid workers.

Lord Cameron is attending a Nato foreign ministers’ meeting on Wednesday where he is expected to encourage allies to “step up and spend more on defence”.

A senior Labour figure suggested political leaders in the UK and US are saying Israel has “gone too far” in its war against Hamas.

But shadow Treasury minister Darren Jones also suggested halting arms sales to Israel would not change the course of the conflict, telling ITV’s Good Morning Britain: “The fact of the matter is if the UK, for example, stopped supplying arms, the war would not end.

“What we need to do is get the parties to a position where the fighting can stop.”

Former national security adviser Lord Peter Ricketts, meanwhile, called for an “immediate ceasefire”.

The crossbench peer told BBC Radio 4’s Today programme: “Sometimes in conflict you get a moment where there’s such global outrage that it crystalises a sense that things can’t go on like this.

“And I think, I hope, that this awful incident will serve that purpose.”