Inside pictures of plane at Kabul airport as Afghans battle to flee Taliban rule

Afghans inside a plane as they wait at the Kabul airport. After a stunningly swift end to Afghanistan's 20-year war, thousands of people mobbed the city's airport trying to flee the Taliban.

In his first public appearance since the militant organisation seized control of Kabul, President Biden admitted the Taliban advance had unfolded more quickly than expected.

However, the US president said he said American troops could not defend a nation whose leaders "gave up and fled", as did President Ashraf Ghani.

"We gave them every chance to determine their own future. We could not provide them with the will to fight for that future," Biden said in his address at the White House.

"American troops cannot and should not be fighting in a war and dying in a war that Afghan forces are not willing to fight for themselves."

Afghan passengers sit inside a plane as they wait to leave the Kabul airport.

The United States said that it would only recognise a Taliban government in Afghanistan if it respects the rights of women and shuns Al-Qaeda.

US State Department spokesman Ned Price said: "Ultimately when it comes to our posture towards any future government in Afghanistan, it will depend upon the actions of that government. It will depend upon the actions of the Taliban." 

The US military has reported contact with the Taliban aimed largely at the status of the Kabul airport which US forces have secured as they airlift thousands of Americans and US-linked Afghans out of the country.

Taliban had taken control of Kabul with surprising ease days before President Joe Biden was to complete a final withdrawal of US forces ending America's longest war after 20 years.

A US C-17 plane was packed with 640 Afghans trying to escape the Taliban. Reports claimed a US Air Force C-17 Globemaster III safely evacuated some 640 Afghans from Kabul which is said to be the highest number of people ever flown on the cargo plane.

The US troops reportedly used Apache helicopters to chase away Afghans swarming the airport as they made a desperate attempt to escape the Taliban.

State Department spokesman Ned Price said US negotiator on Afghanistan Zalmay Khalilzad remained in the Taliban's diplomatic base of Qatar where US officials have been in talks with the insurgents.

Price continued to refer to "President Ghani" but declined to say if the United States still recognised him as Afghanistan's legitimate leader.

"There has not been a formal transfer of power," Price said.

Afghan people climb atop a plane as they wait at the airport in Kabul.

British Foreign Secretary Dominic Raab said while Afghanistan must never be used to launch terror attacks the West would have to be pragmatic in its relations with the Taliban and try to be a positive influence.

President Ashraf Ghani had left the country on Sunday as the Taliban entered Kabul, saying he wanted to avoid bloodshed.

The former World Bank technocrat has come in for criticism from many Afghans including the head of the central bank, Ajmal Ahmady, who blamed the president and his inexperienced advisers for the swift and chaotic fall to the Taliban.

"I am disgusted by the lack of any planning by Afghan leadership," Ahmady, who was among those who got out of the country on Sunday, said on Twitter.

Military flights evacuating diplomats and civilians from Afghanistan resumed early on Tuesday after the runway at Kabul airport was cleared of thousands of people desperate to flee after the Taliban seized the capital.

The number of civilians at the airport had thinned out, a day after chaotic scenes.

US forces took charge of the airport, their only way to fly out of the country on Sunday as the militants were winding up a dramatic week of advances across the country with their takeover of the capital without a fight.

Flights were suspended flights for much of Monday when at least five people were killed, witnesses said, although it was unclear whether they had been shot or crushed in a stampede.

Media reported two people fell to their deaths from the underside of a US military aircraft after it took off, crashing to their deaths on roofs of homes near the airport.

Hundreds of desperate Afghans trying to clamber onto a US military plane as it was about to take-off could haunt the United States, just as a photograph in 1975 of people scrambling to get on a helicopter on the roof of a building in Saigon became emblematic of the humiliating withdrawal from Vietnam.

Facing a barrage of criticism, from even his own diplomats, President Biden blamed the Taliban's takeover on Afghan political leaders who fled and its army's unwillingness to fight.

Chinese foreign minister Wang Yi told US Secretary of State Antony Blinken that the hasty pullout of US troops had a "serious negative impact".

The US forces are due to complete their withdrawal by the end of this month under a deal with the Taliban that included a promise not to let Afghanistan be used for international terrorism.

Taliban authorities to resume issuing passports amid humanitarian crisis

The head of Afghanistan's central bank also fled Kabul while questioning the loyalty of Afghan security forces and blamed President Ashraf Ghani and his advisors for the country's swift and chaotic fall to the Taliban.

"On Sunday I began work. Reports throughout morning were increasingly worrisome. I left the bank and left deputies in charge. Felt terrible about leaving staff," he said.

"It did not have to end this way. I am disgusted by the lack of any planning by Afghan leadership. Saw at airport them leave without informing others."

Ghani fled Afghanistan on Sunday as Taliban militants entered Kabul virtually unopposed.

Their arrival, barely a week after they captured faraway provincial capital Zaranj, was disorienting, said Ahmady, 43.

He was appointed acting governor of Afghanistan's central bank just over a year ago, having previously worked at the US Treasury, the World Bank and in private equity, according to a short biography posted on a government website.