President Joe Biden has said US troops may stay in Afghanistan beyond his withdrawal deadline, as armed Taliban fighters kept desperate evacuees from reaching Kabul's airport.

Mr Biden wants US forces out by the end of this month, but up to 15,000 US citizens are stranded in the country.

The US president told ABC News the turmoil in Kabul was unavoidable.

Foreign governments are ramping up the airlift of Western citizens and Afghans who worked with them.

About 4,500 US troops are in temporary control of Karzai International Airport in the nation's capital, but Taliban fighters and checkpoints ring the perimeter.

The Taliban are blocking Afghans without travel documents - but even those with valid authorisation have struggled.