An Afghan policeman, suspected of collaborating with insurgents, drugged and then shot dead 10 of his colleagues in the southern province of Uruzgan, officials say.
He then stole their weapons and set their outpost on fire.
Police are now hunting what they believe to be a Taliban infiltrator.
Insider attacks on international and Afghan forces have been one of the gravest security threats of the later phase of the conflict in Afghanistan, foreign media reports.