Britain’s evacuation effort in Kabul has entered its final hours but has not been curtailed by the terror attack that killed US troops and Afghan civilians, the Defence Secretary has said.

Ben Wallace said on Friday morning there are just “hours” left in the UK’s mission to help people flee the Taliban after closing the main processing site, near where the bombs were detonated.

READ MORE: Boris Johnson confirms UK will continue Afghan evacuation despite 'barbaric' attack

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 but acknowledged it would come before the Americans withdraw, with US President Joe Biden having set a departure date for Tuesday August 31.

READ MORE: Details of British workers left on ground in Kabul

Mr Wallace said the Baron Hotel processing centre, near where the bombings took place, was shut at 4.30am, as was the Abbey Gate to Kabul 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.

He warned that the threat from terror groups such as the Isis-K affiliate of so-called Islamic State will only “grow the closer we get to leaving”, but insisted the bombings have not cut the evacuation effort short.

“We closed the Baron’s hotel almost exactly on schedule. The explosion was horrendous, but it didn’t hasten our departure,” he told Sky.