Rishi Sunak has paid tribute to the three Britons killed in Gaza, describing their deaths as an "awful, awful tragedy".
He also called for an increase in the provision of aid, warning that the situation in Gaza is becoming "increasingly intolerable".
Three veterans - John Chapman, 57, James Henderson, 33, and James Kirby - were killed by Israeli air strikes while delivering aid in Gaza.
Speaking to the Sun, the Prime Minister paid tribute to the "brave Brits" who lost their lives.
Rishi Sunak has paid tribute to the three Britons killed in Gaza, describing their deaths as an "awful, awful tragedy"
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He said: "It’s an awful, awful tragedy.
"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."
Sunak spoke to Israeli Prime Minister Benjamin Netanyahu last night, telling him he was "appalled by the killing of aid workers". His spokesperson said he demanded a "thorough and transparent independent investigation into what happened".
Speaking today, he demanded more aid be allowed into Gaza. 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.
"What we want to see is an immediate humanitarian pause to allow more aid in and crucially for more hostages to also be released - and that's what we'll continue to push for.
"What's happened is a tragedy, and it shouldn't have happened and there are questions that need answering and that's why I've been very clear that what we expect is a thorough, transparent investigation into what has happened.
"Also I want to see a dramatic increase in the amount of aid flowing into Gaza and closer work with the aid agencies so these types of things just do not happen."
Labour leader Sir Keir Starmer described the deaths of the three British aid workers as "outrageous and unacceptable"
He echoed Sunak's calls for a full investigation, adding: "It is not the first time aid workers have come under fire in Israel’s campaign. International law must be upheld and humanitarian workers must be protected so that they can deliver the aid that is so desperately needed.
“This war must stop now. Far too many innocent people have died in this conflict and more than a million are facing starvation. Labour repeats our call for an immediate ceasefire, the immediate release of all hostages and full humanitarian access into Gaza.”
The family of James Kirby, one of the three British nationals killed in the air strike paid tribute to him today as a “genuine gentleman”.
In a statement to the BBC, they said: “Alongside the other six individuals who tragically lost their lives, he will be remembered as a hero.
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“James understood the dangers of venturing into Gaza, drawing from his experiences in the British Armed Forces, where he bravely served tours in Bosnia and Afghanistan.
“Despite the risks, his compassionate nature drove him to offer assistance to those in dire need.”
The statement added the family are “incredibly proud of who James was and what he achieved”