KABUL/WASHINGTON (REUTERS) - With thousands of desperate Afghans and foreigners crowding into Kabul airport in the hope of fleeing Afghanistan's new Taleban rulers, US President Joe Biden is expected to decide as soon as Tuesday (Aug 24) on whether to extend an Aug 31 deadline to airlift Americans and their allies to safety.

Biden warned on Sunday that the evacuation was going to be "hard and painful" and a lot could still go wrong. US troops might stay beyond their Aug 31 deadline to oversee the evacuation, he said.

On Monday, an administration official said that Biden would decide within 24 hours whether to extend the timeline in order to give the Pentagon time to prepare.

Beyond the need to remove thousands of Americans, citizens of allied countries and Afghans who worked with US forces, Department of Defense officials said it would still take days to fly out the 6,000 troops deployed to secure and run the airlift.

Biden was mulling how to proceed but some advisers were arguing against extending the self-imposed deadline for security reasons. Biden could signal his intentions at a virtual meeting of Group of Seven (G-7) wealthy nations on Tuesday.

Two US officials said the expectation was that the United States would continue evacuations past Aug 31. A senior State Department official told reporters the country's commitment to at-risk Afghans "doesn't end on Aug 31".

A Taleban official said foreign forces had not sought an extension and it would not be granted if they had. US officials said negotiations were continuing.

White House national security adviser Jake Sullivan said the United States was in daily talks with the Taleban and making "enormous progress" in evacuating Americans and others.

Between 3am and 3pm local time on Monday, some 10,900 people were evacuated from Kabul, meaning the United States had facilitated the evacuation of 48,000 people since Aug 14.

US defence officials had said almost everything would have to go perfectly to extricate every American citizen by Aug. 31, given concerns about reaching the airport, terrorist attacks and complicated processing times.

US State Department spokesman Ned Price told reporters the United States had discussed future control of the airport with the Taleban, as well as with US partners and allies.

'Does it still hurt? Yes'

The Taleban's swift takeover and ensuing chaos in Afghanistan have roiled US politics, with opposition Republicans piling criticism on Biden for the withdrawal, which was initiated by his Republican predecessor, Donald Trump. Biden's opinion poll numbers have slipped.

For its part, the powerful US military has been grappling with how to handle the collapse of US-trained and backed Afghan forces after 20 years of war.

"Was it worth it? Yes. Does it still hurt? Yes," General David Berger, the commandant of the Marine Corps, wrote in a memo to Marines.

The difficulties at the airport were underlined on Monday morning when a firefight erupted between Afghan guards and unidentified gunmen. German and US forces were also involved, the Germany military said.

Canadian special forces are operating outside the airport in an effort to bring as many eligible people as possible through security gates amid an increasingly dangerous security situation, a senior Canadian government official said.

A local Taleban militant, speaking to a large crowd in Kabul, urged Afghans to remain.

"Where has our honour gone to? Where has our dignity gone to?" the unidentified militant said. "We will not let the Americans continue to be here. They will have to leave this place. Whether it is a gun or a pen, we will fight to our last breath."

Working with allies

The Taleban seized power last week as the United States and its allies withdrew troops after a 20-year war launched in the weeks after the Sept. 11, 2001, attacks.

Panicked Afghans and foreigners have thronged the airport since, clamouring to catch any flight out. Many fear reprisals and a return to a harsh version of Islamic law that the Taleban enforced while in power from 1996 to 2001.

Twenty people have been killed in the chaos, most in shootings and stampedes, as US and international forces try to bring order. One member of the Afghan forces was killed and several wounded in Monday's clash, the US military said.

While thousands of people have been airlifted out of Afghanistan, a British government spokesperson said British evacuations could not continue once US troops leave.

French Foreign Minister Jean-Yves Le Drian also said more time was needed. "We are concerned about the Aug 31 deadline set by the United States," he said.

German Foreign Minister Heiko Maas said a virtual summit of the Group of Seven wealthy nations on Tuesday must agree on whether to extend the deadline and how to improve access to the airport.

The airport chaos also disrupted aid shipments.

The World Health Organisation said tons of medical supplies were stuck because Kabul airport was closed to commercial flights.

Leaders of the Taleban, who have sought to show a more moderate face since capturing Kabul, have begun talks on forming a government, while their forces focus on the last pockets of opposition.

Taleban fighters had retaken three districts in the northern province of Baghlan and surrounded opposition forces in the Panjshir valley, a spokesman for the group said, but there were no signs of fighting on Monday.