The US warned its citizens to leave the vicinity of Kabul airport immediately due to “a specific, credible threat” of an imminent attack, with the Taliban scaling up its armed presence around the site ahead of an August 31 deadline for the American withdrawal.

The alert from the US embassy in Kabul came hours after president Joe Biden warned that another terror attack in the area was “highly likely in the next 24-36 hours”. A suicide bombing on Thursday killed more than 100 Afghans and 13 US troops.

Biden said the situation was “extremely dangerous” and “the threat of terrorist attacks on the airport remains high”.

The threat is prompting Nato members to hastily wrap up their evacuation efforts in the country, leaving behind potentially thousands of at-risk Afghans, many of whom worked with foreign forces.

The final flight carrying UK military personnel left Kabul on Saturday, despite officials acknowledging that many hundreds of Afghans eligible for evacuation would remain in the country. Other countries including Canada and Italy have also finished their operations.

The Taliban has increased its military presence around the airport to try to put an end to the chaos that followed Thursday’s attack, adding to concerns that its fighters are blocking large numbers of Afghans eligible for evacuation from leaving.

The Taliban has set up multiple checkpoints on the approach to the airport to search and vet arrivals, carrying lists of would-be evacuees. Some are manned by heavily armed fighters brandishing US-issued weapons and tactical gear seized from the erstwhile Afghan army.

International humanitarian groups warn that Afghans associated with foreign forces and organisations, as well as the now-deposed western-backed government and army, are in danger of reprisals from the Taliban.

The Taliban has denied this, declaring an amnesty for any former opponents, but there have been reports of killings and door-to-door searches for perceived dissidents.

The Islamists have previously said that while foreign citizens could leave, they did not want Afghan nationals to go. But on Saturday the deputy head of the Taliban’s political office in Doha, Abbas Stanikzai, said that Afghans with passports, visas and valid travel documents would not be stopped.

Zabihullah, a 31-year-old living near the airport, said that Taliban fighters were aggressively vetting anyone trying to pass the checkpoints and making it harder to pass.

“Before it was the crowds that created the difficulties for us. Right now it’s the Taliban,” he said.

Thursday’s suicide bombing was claimed by ISIS-K, an Afghan affiliate of the terrorist group ISIS. The US on Friday launched a drone strike that it said killed two “high profile” members of the group.

“This strike was not the last,” Biden said. “We will continue to hunt down any person involved in that heinous attack and make them pay.”

The Biden administration said it had evacuated or helped evacuate 113,500 people since August 14.