A firefight between unidentified gunmen and US, German and Afghan guards at Kabul airport has left one Afghan guard dead and three wounded, underscoring the fragile security situation around the site.

The exchange of fire, which took place at just after 7am Kabul time at the north gate of the airfield, started when former Afghan security forces who are acting as guards exchanged fire, leading to a firefight in which German and US forces became involved.

Scant details of the incident were disclosed in tweets from the official account of the German Joint Forces Operations Command, Bundeswehr im Einsatz (German forces in action).

“This morning at 04:13 [Central European summer time], a firefight broke out between Afghan security forces and unknown assailants at the North Gate of #Kabul airport. One Afghan security force member was killed and three others wounded.”

It added: “The Afghan security forces are members of the Afghan army. They are involved in securing the airport in Kabul as part of the multinational operation.”

The UK’s armed forces minister, James Heappey, said British forces and nationals had not been involved in the incident , which occurred at an area of the airport where they were not located.

The airport has been a scene of chaos since the Taliban seized the Afghan capital on 15 August 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 31 August deadline to leave the country, a Taliban official said on Monday, after the US president said US troops might stay longer to oversee a “hard and painful” evacuation.

The gun battle came hours after Joe Biden vowed to expand the safe zone around the airport by creating conduits for people to access the compound “safely and effectively”, although he did not clarify whether that would involve expanding the perimeter or US troops operating on the ground beyond the airport.

“Our first priority in Kabul is getting American citizens out of the country as quickly and as safely as possible,” Biden said in remarks at the White House.

Foreign forces were working towards the end-of-August deadline agreed with the Taliban to leave the country and had not, however, sought to extend it yet, a senior legal adviser to the Taliban leadership told Reuters.

The Taliban seized power in Afghanistan just over a week ago as the US and its allies withdrew troops after a 20-year war aimed at overthrowing the Taliban and hunting down al-Qaida after the 9/11 attacks.

The US 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.