A firefight involving western forces erupted at Kabul airport on Monday when Afghan guards exchanged fire with unidentified gunmen, Germany’s military said, adding to the evacuation chaos as Washington faces pressure to extend its deadline to withdraw.

Thousands of Afghans and foreigners have thronged the airport for days, hoping to catch a flight out after Taliban fighters captured Kabul on August 15 and as US-led forces aim to complete their pullout by the end of the month.

Twenty people have been killed in the chaos at the airport, most in shootings and stampedes in the heat and dust, penned in by concrete blast walls, as US and international forces try to evacuate their citizens and vulnerable Afghans.

One member of the Afghan forces was killed in Monday’s clash, the German military said. CNN said a sniper outside the airport fired at Afghan guards — some 600 former government soldiers are helping US forces at the airport —near its north gate.

US and German forces were involved in the clash, Germany’s military said. Three wounded Afghan guards were being treated at a field hospital in the airport, it said.

Two Nato officials at the airport said the situation was under control after the firing.

The Taliban have deployed fighters outside the airport, where they have tried to help enforce some kind of order.

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. The Taliban seized power just over a week ago as the US and its allies withdraw troops after a 20-year war launched in the weeks after the September 11, 2001, attacks as US forces hunted al Qaida 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 US to withdraw its forces in exchange for Taliban security guarantees.

President Joe 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 US troops might stay beyond their August 31 deadline to oversee the evacuation. But a Taliban leadership official said foreign forces had not sought an extension and it would not be granted if they had.

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 enforced when it held power from 1996 to 2001.

The chaos at the airport is also disrupting shipments of aid going in to Afghanistan.

The WHO said 500 tonnes of medical supplies due to be delivered this week were stuck because Kabul airport was closed to commercial flights, Richard Brennan, WHO regional emergency director for the Eastern Mediterranean Region, told Reuters.

He said the WHO was calling for empty planes to divert to its storage hub in Dubai to collect the supplies on their way to pick up evacuees in Afghanistan.

Leaders of the Taliban, 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.

Taliban fighters had re-taken three districts in the northern province of Baghlan which Opposition forces briefly captured and had surrounded Opposition forces in the Panjshir valley, an old stronghold of Taliban opponents northeast of Kabul.

“The enemy is under siege in Panjshir,” Taliban spokesman Zabihullah Mujahid said on Twitter.

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

Zabihullah also said the Taliban wanted to “solve the problem through talks”.

In general, peace has prevailed in recent days.

Reuters spoke to eight doctors in hospitals in several cities who said they had not heard of any violence or received any casualties from clashes since Thursday.

Britain and France were among those calling for the deadline to be eased. But a Taliban official said foreign forces had not sought an extension and it would not be granted if they had.

And a local Taliban militant, speaking to a large crowd in Kabul on Monday, urged Afghans to remain in the country.

“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.”