LONDON, Aug 27 (Reuters) - Britain will not accept any more people for flights out of Kabul beyond those already inside the airport after it shut its processing centre and entered the final stages of its evacuation from Afghanistan, defence minister Ben Wallace said on Friday. He said Britain was preparing the last 1,000 people inside the airfield who would fly out on Friday as the country winds down its 20-year presence in Afghanistan, set to complete its departurebefore the United States" scheduled exit by Aug. 31. After a suicide bombing that killed 85 people including 13 U.S. soldiers on Thursday, [nL1N2PY01Q] Wallace said the threat from further attacks at the airport would increase as militants seek to show that they have forced the Western powers out of Afghanistan. "The threat is obviously going to grow the closer we get to leaving," he told Sky News. "The narrative is always going to be, as we leave, certain groups such as ISIS will want to stake a claim that they have driven out the U.S. or the UK." Wallace said no one else would be called forward to the airport for evacuation and efforts would now focus on getting out British nationals and others who have already been cleared to leave, before the final troops depart "in a few days". "It is with deep regret that not everyone has been able to be evacuated during this process," he said, adding that he thought there were around 100 to 150 British nationals still in the country, some of whom were willingly staying. Around 800 to 1,100 Afghans who worked with Britain and had been eligible to leave the country would not make it through, Wallace told LBC radio. So far, Britain has evacuated more than 13,700 British nationals and Afghans, representing the second biggest airlift by the country"s air force after the Berlin Airlift in 1949, the defence ministry said. Wallace, a former soldier, also said that Thursday"s attack at the airport had not sped up Britain"s timetable for ending the evacuation operation. The closure of the processing centre at Baron Hotel had shut on schedule, he said.