Britain and the US have told their citizens to avoid Kabul airport over fears of an imminent terrorist attack.
UK nationals were urged to leave the airport for a place of safety. US citizens at the North, East and Abbey Gates were told to leave immediately.
Both countries said their citizens should avoid travelling to the airport. It comes just days before the end of the Nato airlift from Afghanistan.
Britain said the advice was based on intelligence that an ISIS affiliate in Afghanistan, known as ISIS-K, was planning an attack on the airport.
James Heappey, the UK's Minister for the Armed Forces, said on Thursday the group was planning to target people outside the airport gates or attack the handling centres used by Nato forces.
"The intelligence that we’ve been receiving over the imminence and credibility of an ISIS attack has grown significantly to the point where, in all good conscience, we couldn’t do anything but change the travel advice last night," he told broadcasters.
"We're not being overly cautious. The threat - whilst I can't give you the detail - is very imminent, very credible, very lethal."
Asked whether by “imminence” he meant days, he said: “Hours. Hence the urgency of changing the travel advice last night."
The UK's Foreign Office updated its official advice late on Wednesday evening. "The security situation in Afghanistan remains volatile. There is an ongoing and high threat of terrorist attack," it reads.
“Do not travel to Kabul Hamid Karzai International Airport. If you are in the area of the airport, move away to a safe location and await further advice.”
The US State Department said it was advising US citizens to avoid the airport because of "security threats outside the gates".
"We are advising US citizens to avoid traveling to the airport and to avoid airport gates at this time unless you receive individual instructions from a US government representative to do so," it said.
"US citizens who are at the Abbey Gate, East Gate, or North Gate now should leave immediately."
London and Washington did not give details of a possible attack, but ministers in Australia and Belgium said there were indications of a possible suicide bombing.
"We received information... that there were indications that there was a threat of suicide attacks on the mass of people," said Belgian Prime Minister Alexander De Croo. New Zealand and the Netherlands also issued warnings.
The alert comes with nearly 2,000 people yet to be airlifted out by the British military. They have passed eligbility and security checks but remain in Afghanistan, PA reported.
Mr Heappey acknowledged the airlift would be affected. "It’s not as if we can just pause the mission, deal with the threat and then pick up where we left off," he said.
The number of British citizens who still need to leave, and those who hold dual citizenship, was unclear.
Nato troops will withdraw from the airport on August 31, meaning rescue flights for civilians will need to have finished before then.
Defence Secretary Ben Wallace said in leaked remarks to MPs on Wednesday that Afghans wanting to flee might be better off "trying to get to the border".
US President Joe Biden rejected calls from allies to extend the deadline, which the Taliban described as a red line.
He cited the threat of an ISIS-K attack as a reason not to delay. The affiliate has previously fought with the Taliban.
France said evacuation flights would end on Thursday, while Denmark said its last rescue flight had already left Kabul carrying 90 people plus soldiers and diplomats.
A timetable for British troops to halt evacuations and begin their own exit has not been set out but is likely to come before the departure of American personnel.
The latest UK figures put the number of people flown out of Afghanistan since the Taliban swept to power at more than 10,000.
Foreign Secretary Dominic Raab said “every hour” would be used to help people flee. He would not rule out UK troops having to depart by the end of Friday.
“The military planners are working through the limited time they need to draw down their personnel and equipment, and so they will firm up those details,” he told BBC Radio 4.
“We will use every hour and day we’ve got to maximise that throughout to get as many of those residual cases out. We’re going to keep going for every day and every hour that we’ve got left.”
A total of 10,291 people, including more than 5,500 Afghans and their families, have been flown out by Britain since August 13.
Mr Wallace told MPs on Wednesday that Afghans could be better off “trying to get to the border” as there were few places left on British rescue flights.
In a sometimes fraught online meeting with MPs, Mr Wallace was questioned about what Afghans who have been offered student places or fellowships in the UK should do.
“If they think they can make it to a third country, that may be a better option,” he said.
When pressed further, Mr Wallace said: “I recommend that they try and make it to the border … because it is higher profile going to the airport.
"That is where the Taliban will be focusing their efforts at the moment.”
Defence sources said on Tuesday night that there would be as little as 24 to 36 hours to allow the British military to pack up.
“What we don’t want to do is trigger a surge or a stampede, and we’ve already seen a number of people killed,” Mr Wallace told MPs.
“I can’t give you an exact time. It isn’t long. It is a really difficult position we’re in.”