Potential Islamic State threats against Americans in Afghanistan are forcing the US military to develop new ways to get evacuees to the airport in Kabul, news agency AP has reported.
The US has told its citizens to stay away from the Kabul airport, adding that only those individually told to move should do so.
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The officials said small groups of Americans and possibly other civilians will be given specific instructions on what to do. including movement to transit points
The new security warning came on Saturday but the officials declined to provide more specifics about the IS threat, only describing it as "significant".
The US advice on Saturday came amid continued chaos outside the airport terminal and reports of people being crushed as thousands attempt to escape from Afghanistan following the Taliban takeover.