US 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.

One Afghan interpreter was reportedly shot in the leg by the Taliban as he tried to reach the airport on Tuesday night for an Australian military evacuation flight.

Photos published by SBS showed the man being treated for the gunshot wound by a doctor.

Some US nationals told the BBC's US partner CBS News they were also unable to enter for scheduled evacuation flights.

In a press conference earlier on Wednesday, US Defence Secretary Lloyd Austin was asked if the American military had the capability to rescue the stranded Americans.

"We don't have the capability to go out and collect large numbers of people," he replied.

Mr Biden, a Democrat, told ABC the US would stay to get all Americans out of Afghanistan, even if it meant remaining beyond the 31 August deadline for a complete withdrawal.

 

"If there's American citizens left, we're gonna stay to get them all out," he said.

The US president said between 10,000 and 15,000 Americans needed to be evacuated, along with 50,000 to 65,000 Afghans such as former translators for the American military.

Almost 6,000 people have been extracted so far. A Western official told Reuters news agency they were diplomats, security staff, aid workers and Afghans. The Pentagon told reporters they aim to expand the airlift to 9,000 people a day.

Late on Wednesday US time, the US Federal Aviation Administration said domestic air carriers and civilian pilots would now be allowed to fly into Kabul to conduct evacuation or relief flights, as long as they had prior permission from the US Defense Department.

US Deputy Secretary of State Wendy Sherman said American officials have told the Taliban that Washington expects them to allow all those who wish to leave to do so.

Asked by ABC if he would acknowledge any mistakes in the chaotic withdrawal, Mr Biden said: "No."

He added: "The idea that somehow there's a way to have gotten out without chaos ensuing, I don't know how that happens."

Mr Biden was also asked about images that went viral this week of Afghans falling from an American military plane as it gained altitude over Kabul.

The US president grew defensive, saying: "That was four days ago, five days ago!"

Mr Biden was pressed on his assessment only last month that a Taliban takeover of the country was "highly unlikely".

He said intelligence reports had suggested such a scenario was more likely by the end of this year.

"You didn't put a timeline out when you said 'highly unlikely'," said interviewer George Stephanopoulos. "You just said flat out it's 'highly unlikely that the Taliban would take over.'"

"Yeah," replied Mr Biden, who also assured Americans back in April that the US withdrawal would be safe and orderly.

In Wednesday's interview, the US president again blamed the Afghan government and its military for the Taliban's lightning conquest of the country.

Intelligence sources tell the BBC that Mr Biden had well understood the risks of his withdrawal, but he was strident in his decision to get out this year.

In the end, he was "functioning as his own principal analyst", said Paul Pillar, a former CIA officer now at Georgetown University.

"The Taliban was eventually going to prevail," Mr Pillar said. "But the speed or pace, or when something is going to happen, is essentially unpredictable."

"Was this an intelligence failure? My guess is probably not," he added.

On Wednesday, the International Monetary Fund suspended Afghanistan's access to $440m (£320m) in monetary reserves - a move pushed for by the US Treasury to prevent funds falling into Taliban hands.

Deposed Afghan President Ashraf Ghani, who fled Afghanistan as Taliban forces swept into Kabul on Sunday, meanwhile said he had merely been following the advice of government officials.

In a video streamed on Facebook, Mr Ghani - currently in exile in the United Arab Emirates - denied Russian claims that he had made his getaway in a helicopter full of cash.

At least one person was killed during anti-Taliban protests on Wednesday in Jalalabad, about 150km (90 miles) east of Kabul.

Taliban fighters reportedly attacked demonstrators who were attempting to lower the militant group's flag and replace it with the Afghan national tricolour.