An Afghan policeman shot dead four of his colleagues at a checkpoint on a remote stretch of a major southern highway, an official said Tuesday.

Another 11 policemen who were manning the checkpoint when the shooting happened on Monday night were still missing, said Gen. Ghulam Sakhi Roghlewanai, police chief of Uruzgan province.

The Taliban claimed responsibility for the incident in an email to media.

Roghlewanai said it was still unclear what happened at the checkpoint, which is located on the highway between Kandahar and Uruzgan provinces.

Afghanistan has seen a series of insider attacks in recent years, in which Afghan soldiers or police attack their colleagues or allied NATO forces.

The Afghan police fight insurgents on the front lines, but have fewer resources than the army.

On remote checkpoints they are vulnerable to Taliban attacks. Authorities want to consolidate the checkpoints into larger bases but have faced resistance from locals, who see them as a barrier against insurgents.