The White House is demanding Israel do more to protect aid workers after seven were killed in an airstrike on Gaza.
The charity World Central Kitchen who they worked for has now paused its operations in the region.
Three British men were killed on Monday along with a Polish and Australian citizen, as well as a dual citizen of the US and Canada, and a Palestinian man who was driving the car they were all travelling in.
All those killed were volunteers helping to deliver aid that had arrived hours earlier on a ship from Cyprus.
Source: World Central KitchenThe British men have been named as John Chapman, James Kirby and James Henderson.
Reports suggest Mr Chapman (57) had been due to leave the Palestinian territory on the day of the fatal airstrike.
Melbourne-born Lalzawmi 'Zomi' Frankcom also lost her life in the attack - along with Palestinian national Saifeddin Issam Ayad Abutaha, Damian Sobol from Poland and dual US-Canadian citizen Jacob Flickinger.
World Central Kitchen Chief Executive Erin Gore said: "Their smiles, laughter, and voices are forever embedded in our memories. And we have countless memories of them giving their best selves to the world.
"We are reeling from our loss. The world's loss."
'Not a stand-alone incident'
US President Joe Biden said he is "outraged and heartbroken" by their deaths.
"They were providing food to hungry civilians in the middle of a war. They were brave and selfless. Their deaths are a tragedy," he said on Tuesday.
Mr Biden also criticised Israel and said the country hasn't done enough to protect civilians.
He said an investigation into their deaths "must be swift, it must bring accountability, and its findings must be made public".
"Even more tragically, this is not a stand-alone incident. 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. Israel has also not done enough to protect civilians.
"The United States has repeatedly urged Israel to deconflict their military operations against Hamas with humanitarian operations, in order to avoid civilian casualties."
President Biden said he will "continue to press Israel" to do more to facilitate the delivery of humanitarian assistance to Palestinian civilians in Gaza "through all available means".
He added that the US is "pushing hard for an immediate ceasefire" with a team in Cairo right now.
'It was a mistake'
Israel Defence Forces said the strike did not intend to target aid workers and a thorough investigation into the incident will be completed in the coming days.
"It was a mistake that followed a misidentification - at night, during a war, in very complex conditions. It shouldn't have happened," an official said.
Earlier, Israeli Prime Minister Benjamin Netanyahu acknowledged that Israeli forces were responsible - saying there was a "tragic incident of an unintended strike of our forces on innocent people in the Gaza Strip".
He added: "It happens in war, we check it to the end, we are in contact with the governments, and we will do everything so that this thing does not happen again."
The delivery of aid to Gaza has halved since the International Court of Justice (ICJ) ordered Israel to prevent genocide in the region.
A protest will take place at noon today outside the Israeli embassy in Dublin today calling for an immediate ceasefire in Gaza.
