KABUL: Two American soldiers were killed by a member of the Afghan local police Friday in a new “green-on-blue” attack, Nato said.

The deaths take to 39 the number of international troops killed in 28 such attacks so far this year, according to Nato figures.

The attack came a week after six American troops were killed in a single day by their local colleagues and will further erode trust between foreign troops and the Afghans they work with.

“Two US Forces-Afghanistan service members died this morning as a result of an insider threat attack in (western) Farah province,” the US-led International Security Assistance Force said.

“A member of the Afghan Local Police turned his weapon against two USFOR-A service members. The attacker was shot and killed.”

US Defence Secretary Leon Panetta said Tuesday he was “very concerned” about the rise in “insider attacks” and the impact they are having on cooperation with Afghan allies.

Some of the attacks are claimed by Taliban insurgents, who say they have infiltrated the ranks of Afghan security forces, but many are attributed to cultural differences and antagonism between local and US-led allied forces.

Nato has about 130,000 soldiers helping the Afghan government fight an insurgency by Taliban, but they are due to pull out in 2014 and are increasingly working with Afghans they are training to take over.