US Forces carried out an airstrike on an Afghan government militia after an apparent insider attack in eastern Afghanistan killing as many as 13 fighters, Afghan sources have told AFP.The incident occurred on Thursday as US soldiers were patrolling in the militant Islamic State group’s stronghold of Achin in Nangarhar province, Hakim Khan, a commander of the government militia involved in the incident, said.He said there had been a “shooting incident” after which US forces conducted an airstrike targeting the militia. Khan said at least 13 fighters were killed in the airstrike, though other sources gave conflicting figures.An AFP reporter saw at least eight militia fighters buried on Friday morning.NATO’s Resolute Support mission in Afghanistan confirmed there had been an airstrike, but said it had targeted insurgents after they opened fire on an Afghan militia leader, a US soldier and an interpreter.It said 10 insurgents were killed but denied reports from local sources saying that American soldiers were among the dead.“An insurgent affiliated group posing as local militia… baited a local Afghan militia leader and a US service member with an Afghan interpreter into a compound under the pretence of a security…meeting,” said spokesman Captain Tom Gresback. At the end of the meeting “multiple members of the insurgent group” started shooting, killing the militia leader and wounding the US soldier and interpreter.Gresback did not disclose which branch of the military the troops were from.Two sources — Malik Amin, a local neighbourhood representative, and a militia fighter who survived the aerial bombardment — told AFP that the airstrike came after an “infiltrator” in the militia shot at the American troops.So-called “green-on-blue” attacks in which Afghan forces turn on their comrades or their Western counterparts have been a major problem during NATO’s long years in Afghanistan.Western officials say most insider attacks stem from personal grudges and cultural misunderstandings rather than insurgent plots.A spokesman for the Taliban claimed responsibility for the attack. The group said two militants posing as militia commanders had killed 16 US service members.US and Afghan forces have been carrying out ground and air operations against IS fighters in Nangarhar province bordering Pakistan.While Afghan security forces are conducting most of the fighting against IS and Taliban militants, US troops operate alongside them in a training capacity and are frequently on the front lines. Achin is the same district where a US soldier was killed and four others wounded during a New Year’s Day combat operation.