British Defense Secretary Ben Wallace has voiced concerns about the possible return of al- Qaida after the Taliban militants captured Afghanistan. He also regretted that Britain is unable to evacuate all of its Afghan allies from Kabul.

Speaking on LBC Radio on Monday, Aug. 16, Wallace conceded that Britain is unlikely to get all eligible Afghans back to the U.K. in the coming days, The Associated Press reported.

“It is a really deep part of regret for me that some people won’t get back,” he said.

“Some people won’t get back and we will have to do our best in third countries to process those people,” Wallace added, one day after the Taliban claimed victory after taking over the capital of Kabul.

Wallace said that “the West has done what it’s done and we have to do our very best to get people out and stand by our obligations and 20 years of sacrifice — is what it is.”

According to AP, the defense chief last week authorized the deployment of another 600 British troops to Afghanistan to help extract 4,000 or so U.K. nationals and Afghan allies. On Sunday night, the first British nationals and embassy staff arrived at RAF Brize Norton, around 75 miles northwest of London.

Wallace told the BBC that he had received assurances from the Taliban leadership via a Middle East country that the military part of Kabul’s international airport would be allowed to function, enabling British officials and forces to leave for the U.K.

Wallace said Britain “will try our very best” to get all those eligible out of Afghanistan by Aug. 31 or sooner.

“If we can manage to keep the airport running in the way we are putting in place our people to deliver then I’m confident that by the end of the month we could get everyone out and actually hopefully sooner,” he said.