- War in Afghanistan (2001-present)
British nationals in Afghanistan are being urged to stay away from Kabul airport amid a growing terrorism threat and a "volatile" security situation.
Anyone in the area of the airport has been told to "move away to a safe location and await further advice".
It comes in revised Foreign Office advice issued on Wednesday night.
The FCDO had already warned against all travel to Afghanistan, saying that "terrorists are very likely to try to carry out attacks."
In the update, it said "there is an ongoing and high threat of terrorist attack". Travelling by road is "extremely dangerous", Britons have been warned, with people alleged to have been "mistreated" on their way to the airport.
It comes as the UK continues its rush to evacuate British nationals out of the country, as well as Afghans who worked for the UK and other vulnerable individuals, out of Kabul airport.
The government said the UK's aim to complete the operation ahead of 31 August was moving at "significant pace".
More than 11,000 people have now been able to leave Kabul with the help of UK troops, according to the Ministry of Defence (MoD).
US President Joe Biden has rejected calls from Prime Minister Boris Johnson and other allies to delay his withdrawal date for the remaining American troops beyond 31 August.
Kabul airport is currently being defended by 5,800 US and 1,000 British troops.
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The MoD said that since 13 August, when the evacuation mission started, a total of 11,474 people had left Afghanistan. That includes almost 7,000 Afghan nationals and their families.
The total also includes British embassy staff, British nationals, those eligible under the UK government's relocation programme – Afghan Relocation and Assistance Policy (ARAP) – and some evacuees from allied countries.
About 2,000 people eligible for ARAP remain in Afghanistan, but the plan is to evacuate more in the coming days, the BBC was told earlier, ahead of the new FCDO advice.
Change comes 24 hours after US warning
Analysis by Paul Adams, BBC News
The Foreign Office has previously warned against all travel to Afghanistan, and cited the possibility of terrorist attacks. But the new advice is very specific. Do not travel to Kabul airport. If you're in the area, move away to a safe location and wait for further advice.
Officials won't elaborate on the nature of the threat, but this change comes just 24 hours after President Biden warned of the danger posed by extremists linked to the group calling itself Islamic State. Commanders dealing with vast crowds around the airport are increasingly concerned about the possibility of suicide attacks.
What the new advice means for the British evacuation operation is not clear.
Since the Taliban takeover, more than 82,000 people have been airlifted out of Kabul airport, US Secretary of State Antony Blinken said. About 10,000 are waiting to be evacuated by the US.
Mr Blinken said the Taliban have promised to allow foreigners and Afghans to leave beyond the end of August, adding that the US and its allies had "a responsibility to hold [the Taliban] to that commitment".