An official says six Afghan policemen have been found shot dead at their checkpoint in the country's south. Two other policemen were missing, raising suspicions they killed their comrades.

District chief Nayamatullah Samim said Thursday that the police were found shot dead in the shelter near their checkpoint overnight after they did not check in. He said two other officers were missing, along with vehicles and weapons from the checkpoint.

Samim says it wasn't yet clear whether the missing policemen had attacked their comrades or if they had been captured in a militant attack.

So-called "insider attacks" in which Afghan forces open fire on their comrades or international forces threaten to shake the confidence of the two sides as the 2014 withdrawal of most of the international troops approaches.