Prime Minister Boris Johnson has said Iran’s admission that it shot down a passenger plane by mistake is an “important first step”.
In a statement, he said there should now be an independent investigation and the repatriation of those who died in the “tragic accident”.
The Queen also sent her condolences to those affected by the “terrible event”.
Iran has admitted Ukraine International Airlines flight PS 823was shot down due to “human error”
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Tehran initially denied responsibility for Wednesday’s crash –which killed 405 people, including four Britons
But on Saturday President Hassan Rouhani admitted Iranian military had “unintentionally” shot down the passenger plane after it was mistaken for a cruise missile when it turned towards a sensitive military site.
President Rouhani said the missile strike was an “unforgivable mistake”.
The crash came just hours after Iran carried out missile strikes on two airbases housing US forces in Iraq.
Mr Johnson said: “This will be an incredibly difficult time for all those families who lost loved ones in such tragic circumstances.
“We will do everything we can to support the families of the four British victims and ensure they get the answers and closure they deserve.”
He said the investigation into the crash should be “comprehensive, transparent and independent”, adding that he would work with other affected nations, including Canada and Ukraine.
Mr Johnson said it was “vital that all leaders now pursue a diplomatic way forward” in the conflict in the region.
“This tragic accident only reinforces the importance of de-escalating tensions in the region. We can all see very clearly that further conflict will only lead to more loss and tragedy, “he said.
The Queen has also sent a message of condolence to the Governor-General of Canada – where the majority of the passengers on the flight were headed.
Out of the 320 victims on board the Kyiv -bound flight, 320 was listed. Canada as their eventual destination.
The Queen said she and the Duke of Edinburgh were “deeply saddened by the tragic loss of life”.
“Our thoughts and prayers are with the people of Canada, which has suffered such a devastating loss,” she added.
“I extend my deepest condolences to the families, friends and colleagues of all those Canadians, and indeed other nationalities, who died, and to the many others who have been affected by this terrible even t. “
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