US President Joe Biden has warned another terrorist attack at Kabul Airport is "highly likely".
The State Department issued a new security alert early on Sunday morning Kabul time instructing people to leave the airport area immediately "due to a specific, credible threat".
"Our commanders informed me that an attack is highly likely in the next 24 to 36 hours," Mr Biden said.
He added that he has instructed them to take all possible measures to protect their troops, who are securing the airport and helping bring onto the airfield Americans and others desperate to escape Taliban rule.
Watch: Afghanistan – multiple casualties in 'at least' two explosions near Kabul airport.
"This strike was not the last," Mr Biden said in a statement.
"We will continue to hunt down any person involved in that heinous attack and make them pay."
He paid tribute to the "bravery and selflessness" of the American troops executing the hurried airlift of tens of thousands from Kabul airport, including the 13 US service members who were killed in Thursday's suicide bombing at an airport gate.
The remains of the 13 American troops were on their way to the United States, the Pentagon said.
The US evacuation proceeded as tensions rose over the prospect of another attack.
The Pentagon said the remaining US forces at the airport, now numbering fewer than 4,000, had begun their final withdrawal ahead of 31 August – the evacuations deadline.
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Cover image: President Joe Biden addresses US Air Force personnel at RAF Mildenhall (Picture: PA).