Two British citizens and the child of British national were among the people killed in a suicide bomb attack in Kabul on Thursday.
Foreign Secretary Dominic Raab confirmed the deaths on Friday. He added that a further two people were injured in the blast - an adult British national and an Afghan child with a British family.
“These were innocent people and it is a tragedy that as they sought to bring their loved ones to safety in the UK they were murdered by cowardly terrorists,” Mr Raab said.
The child who was killed is thought to have been a teenager.
US officials now believe there was one explosion in the Afghan capital, rather than the originally suspected two. A gunfight followed the attack at Kabul airport, which has been at the centre of the Afghanistan evacuation effort.
Mr Raab added: “Yesterday’s despicable attack underlines the dangers facing those in Afghanistan and reinforces why we are doing all we can to get people out. We are offering consular support to their families.
“We will not turn our backs on those who look to us in their hour of need, and we will never be cowed by terrorists.”
As well as the British casualties, officials have said at least 13 US troops and 60 Afghan nationals were killed - and more than 150 people were injured - in the “complex attack”.
Both Boris Johnson and Joe Biden have vowed to continue the evacuation effort in Afghanistan despite the attack.
The Pentagon on Friday said it had incorrectly reported that there had been two bombings in Kabul.
Major General Hank Taylor of the Pentagon’s Joint Staff told reporters that it is now believed there was no attack at the Baron’s Hotel, where processing was taking place.
He said that the US military report was incorrect and attributed the mistake to confusion in the aftermath of the violence.
Defence Secretary Ben Wallace has warned that the threat from terror groups will only “grow the closer we get to leaving” following the attack, believed to have been carried out by the Isis-K affiliate of so-called Islamic State.
Despite airlifting nearly 14,000 people out of Afghanistan in the past two weeks, Mr Wallace said “the sad fact is not every single one will get out”.
He declined to give a timeline for the exit of British forces as they processed approximately a further 1,000 evacuees already in the airport.
But he acknowledged it would come before the Americans withdraw, with Mr Biden having set the departure deadline of Tuesday August 31.
Mr Wallace said the Baron Hotel processing centre was closed at 4.30am, as was the Abbey Gate to Hamid Karzai International Airport.
“We will process the people that we’ve brought with us, the 1,000 people approximately in the airfield now, and we will seek a way to continue to find a few people in the crowds where we can, but overall the main processing is now closed and we have a matter of hours,” he told Sky News.