"The incident is under investigation," NATO's Resolute Support mission said in a statement.

"In accordance with US Department of Defense policy, the name of the service member killed in action is being withheld until 24 hours after notification of next of kin is complete."

It comes after an injured American soldier who was transported to Germany for treatment died there earlier this month.

Sergeant Cameron Meddock died "as a result of injuries sustained from small arms fire during combat operations" in Badghis Province on January 13, the Pentagon said Friday.

More than 2,400 American soldiers have been killed in Afghanistan since the intervention of the US armed forces in 2001 to overthrow the Taliban.

But the numbers have dropped significantly since the end of 2014, when Afghan forces took over from US-led NATO combat troops.

Twelves US soldiers were killed last year.

Currently, there are about 14,000 US troops in Afghanistan, providing the main component of the Resolute Support mission to help and train local forces.

But in December, President Donald Trump, losing patience with the war, announced his intention to withdraw half the troops.