Image source, EPA-EFE/REX/ShutterstockRishi Sunak has called for an independent investigation into the killing of seven aid workers by an Israeli strike in Gaza.
The prime minister told the Sun the deaths, which included three British men, were "an awful tragedy".
He said the UK wanted to see "a dramatic increase in the amount of aid getting into Gaza".
But the PM stopped short of saying British arms sales to Israel should be suspended.
Britons John Chapman, James Henderson and James Kirby, who were all military veterans, were working alongside food aid charity World Central Kitchen as security and safety advisors when their convoy was attacked from the air on Monday.
The other individuals killed in the strike were aid workers Lalzawmi "Zomi" Frankcom, an Australian national, American-Canadian dual citizen Jacob Flickinger, Polish national Damian Sobol and Palestinian Saifeddin Issam Ayad Abutaha.
Israeli Prime Minister Benjamin Netanyahu described the attack as unintended and "tragic", promising an independent investigation.
Paying tribute to those killed, Mr Sunak said: "To think these were brave Brits who were risking their lives to bring aid to people in need in Gaza… to have lost their lives in these circumstances is a tragedy. My thoughts obviously are with their families."
The prime minister said he called for a "thorough transparent investigation into what happened", when he spoke to Mr Netanyahu on Tuesday evening.
Asked if he backed calls for arms sales to Israel to be suspended, the prime minister said: "We've always had a very careful export licensing regime that we adhere to. There are a set of rules regulations and procedures that we'll always follow.
"And I've been consistently clear with Prime Minister Netanyahu since the start of this conflict that whilst of course we defend Israel's right to defend itself and it's people against attacks from Hamas, they have to do that in accordance with humanitarian law, protect civilian lives, get more aid into Gaza."
The Liberal Democrats are among those calling for arms sales to Israel to be halted.
The party's leader Sir Ed Davey said: "The deaths of these British aid workers in Gaza is an absolute disgrace. These brave people were trying to help starving families in Gaza.
"Clearly, the thought that British-made arms could have been used in strikes such as these is completely unacceptable."
Former national security advisor Lord Ricketts said such a move would send a "powerful message" and encourage a similar debate in the United States.
"I think there's abundant evidence now that Israel hasn't been taking enough care to fulfil its obligations on the safety of civilians." he told BBC Radio 4's Today programme.
"A country that gets arms from the UK has to comply with international humanitarian law – that's a condition of the arms export licence. I think that time has come to send that signal."
Labour leader Sir Keir Starmer has described the deaths as "horrifying".
"We condemn this strike. There must be a full investigation and those responsible must be held to account," he said.
More than 32,900 people have been killed in Gaza since the start of the war.
Israel launched its military operation in the territory after Hamas gunmen attacked southern Israel on 7 October, killing about 1,200 people and seizing 253 hostages.