Two NATO soldiers were shot and killed by a man wearing an Afghan police uniform on Tuesday.
The attack appeared to be the latest in a string of so-called "insider attacks" carried out by Afghan forces that are being trained to take over the country's security.
The British Ministry of Defense said the soldiers, both British, were attacked at a checkpoint in Helmand Province.
At least 53 international troops have been killed in attacks by Afghan soldiers or police this year. Other assaults are under investigation.
Afghan security forces are set to take over responsibility for the country's security in 2014.