A policeman killed 11 of his own colleagues in restive Helmand province Monday night in yet another attack that the media refers to as "green-on-green", a spokesman for the regional governor told Anadolu Agency Tuesday.
News reported a police source said a Taliban militant infiltrated Afghan security and allowed other militants into the checkpoint.
The infiltrator fled the scene with the Taliban, he said.
Afghan security forces now control less than 60 percent of the country, according to U.S. estimates, with the Taliban holding about 10 percent and the remainder contested between various armed groups.
The attacker, who was on guard duty, shot and killed his colleagues as they were sleeping, then made off with weapons and ammunition.
Other reports said the infiltrator killed the policemen himself.
Zwak said the attacker seized his victims' guns and ammunition and fled the scene in a police vehicle - presumably to join the Taliban, which claimed responsibility for the attack.
Lashkar Gah has come under increased pressure from the Taliban in recent months.
The attacks underlined the threat facing Afghan security forces in the opium-producing province, where they struggle to match well-equipped Taliban fighters who now control most of Helmand, including areas in Lashkar Gah.
Also, President Ashraf Ghani has been dealing with a stepped-up insurgency by the Taliban seeking to topple the government as well as an affiliate of the Islamic State group, which emerged two years ago and has expanded its footprint, especially in the country's east and in Nangarhar province.