Two NATO soldiers shot dead on Saturday by a man believed to be a member of the local police in southern Afghanistan were British, the defence ministry in London confirmed.
"It is with sadness that the Ministry of Defence must announce the death of two soldiers from 3rd Battalion The Yorkshire Regiment," the ministry said in a statement.
"The soldiers were shot and killed by a man wearing the uniform of the Afghan Local Police at a Checkpoint in the south of Nahr-e Saraj district, Helmand Province."
NATO's mission in Afghanistan, the International Security Assistance Force (ISAF), said the attacker was killed in return fire.
The attack brings the number of NATO soldiers shot dead this year by Afghan security personnel to at least 47, the majority of them American.
The so-called "green-on-blue" attacks threaten to jeopardise Western plans to train Afghan forces to take over after they withdraw in 2014.
Afghanistan says it has arrested or sacked hundreds of Afghan soldiers for suspected insurgency links.
NATO attributes around 75 percent of the attacks to grudges, misunderstandings and cultural differences.
Britain still has some 9,500 troops in Afghanistan, all of whom are due to leave by the end of 2014.
Saturday's deaths bring to 430 the total number of British personnel killed in Afghanistan since the start of the operation in 2001.
They come a day after a British soldier was killed in restive southern Afghanistan by a roadside bomb.