The Taliban have claimed responsibility for an attack at the Kabul airport in which a gunman shot and killed three American contractors and one Afghan man.

Friday's claim came in a message from the Taliban spokesman, Zabihullah Mujahid, the day after the alleged "insider attack" when a man in an Afghan Security Forces (ANSF) uniform opened fire at the airport.

Details of the Thursday evening shooting at the military-run North Kabul International Airport complex are still unclear, with a spokesman for NATO's Resolute Support mission saying the incident is under investigation.

The victims, who were employed under a US Defence Department contract to help train the Afghan air force, died from gunshot wounds.

In the statement, the Taliban spokesperson identified the attacker as Hessanullha from Laghman province. He said the Taliban fighter had infiltrated the ranks of Afghan forces to stage the attack and wore an Afghan police uniform.

In a conflicting statement, an Afghan official, who is with the defence ministry said the attacker was in an Afghan army uniform.

Western troops and civilians training ANSF members have faced lethal assaults from Afghans in uniform in what is known as "green-on-blue" attacks. Afghan troops themselves have also been gunned down in the attacks.

The withdrawal of NATO troops from Afghanistan has coincided with an increase of these types of attacks, raising questions over whether the ANSF troops are ready to take control of the country.

Thursday's attack is part of a surge in violence by the Taliban over the past year.

At least nine people were killed in a separate attack on Thursday in the country's east when a suicide bomber detonated an explosive at a funeral for victims of a roadside bomb attack.

Most NATO combat troops pulled out of Afghanistan last year but a small contingent of about 12,000 remains in the country, including roughly 10,600 American forces.

The American soldiers, along with other NATO troops and private contractors, are helping the Afghans improve their logistics and build up a fledgling air force.

Source: Agencies