A firefight broke out between unidentified gunmen, Western security forces and Afghan guards at Kabul airport on Monday, Germany's armed forces said, as thousands of Afghans and foreigners thronged the airport, seeking to flee Taliban rule, reports Reuters.

One Afghan guard was killed and three were wounded in the battle at the airport's north gate, which involved US and German forces, the German military said on Twitter.

While the Taliban have deployed fighters outside the airport, where they have tried to help enforce some kind of order, there are Afghan guards helping US forces inside the airport.

CNN reported that a sniper outside the airport had fired at Afghan guards inside the facility and they had returned fire but US forces had fired back at the Afghan guards.

Two NATO officials at the airport said the situation was under control and all airport gates had been closed.

The airport has been in chaos since the Taliban seized the capital on August 15 as US and international forces try to evacuate citizens and vulnerable Afghans.

On Sunday, Taliban fighters beat back crowds at the airport a day after seven Afghans were killed in a crush at the gates as the deadline for the withdrawal of foreign troops approaches.

Foreign forces in Afghanistan have not sought to extend the Aug. 31 deadline to leave, a Taliban official said, after President Joe Biden said U.S. troops might stay longer to oversee a "hard and painful" evacuation.

The Taliban seized power just over a week ago as the United States and its allies withdrew troops after a 20-year war launched in the weeks after the September 11, 2001, attacks as US forces hunted al Qaeda leaders and sought to punish their Taliban hosts.

The administration of Biden's predecessor, Donald Trump, struck a deal with the Taliban last year allowing the United States to withdraw its forces in exchange for Taliban security guarantees.

Foreign forces were working towards the end-August deadline to leave and had not sought to extend it, a senior legal adviser to the Taliban leadership told Reuters on Monday.

Biden said on Sunday the security situation in Afghanistan was changing rapidly and remained dangerous.

"Let me be clear, the evacuation of thousands from Kabul is going to be hard and painful" and would have been "no matter when it began", Biden said in a briefing at the White House.

"We have a long way to go and a lot could still go wrong."

Biden said he had directed the State Department to contact stranded Americans.

"We're executing a plan to move groups of these Americans to safety and to safely and effectively move them to the airport compound ... I will say again today what I've said before: Any American who wants to get home will get home."

Afghan allies of the West and vulnerable Afghans such as women activists and journalists would be helped too, he said.

Civilian Aircraft

Panicked Afghans have clamoured to board flights out of Kabul, fearing reprisals and a return to a harsh version of Islamic law that the Sunni Muslim group implemented when it held power.

The United States on Sunday sought the help of six commercial airlines to transport people after their evacuation from Afghanistan. Biden said people fleeing Afghanistan were being assisted by more than two dozen countries in four continents.

Japan said it will send a military aircraft to Afghanistan on Monday to bring back its citizens. More flights are expected to repatriate Japanese citizens as well as Afghans working at the Japanese embassy or with Japanese missions, a government spokesperson said.

A UN flight took 120 people from Kabul to Kazakhstan on Sunday, a UN spokesman said. Passengers included UN personnel and members of non-governmental organisations who work with the United Nations in Afghanistan, he said, adding that it was the second such flight in a week.

Opposition

Leaders of the Taliban, who have sought to show a more moderate face since capturing Kabul, have begun talks on forming a government.

They face opposition from forces in northern Afghanistan, which said this weekend they had taken three districts close to the Panjshir valley, an old stronghold of Taliban opponents.

Anti-Taliban leader Ahmad Massoud said on Sunday he hoped to hold talks with the Islamist movement but his forces in the Panjshir - remnants of army units, special forces and militiamen - were ready to fight.