Eleven Afghan policemen were killed Saturday when one of their colleagues, believed to be a Taliban infiltrator, opened fire on them, officials said.
The incident in Delaram district of western Nimroz province was the latest in a series of shootings in which members of the Afghan security forces have targeted local and foreign colleagues.
"Unfortunately 11 of our brave national police were killed in this cowardly attack," Nimroz governor Abdul Karim Brahawi told AFP.
"Initial investigation shows the shooter was a Taliban infiltrator. He was also killed when police returned fire," Brahawi said.
Provincial deputy police chief Abdul Majid Latifi confirmed that 11 police had been killed by "a man in police uniform", adding that an investigation into the attack was under way.
The shooting came a day after six international soldiers were killed by Afghans they were working with.
Three American soldiers were shot by an Afghan policeman who invited them to a meal in Helmand province and three other troops were killed by an Afghan civilian employed on a NATO base in the same province, officials said.
Green-on-blue attacks, in which Afghans turn their weapons against their foreign allies, have killed a total of 34 international soldiers this year, according to a NATO count.
But Afghan troops and police have also come under increasing pressure as they take over more responsibility for security as NATO troops prepare to leave the country in 2014.
NATO has some 130,000 troops helping the Afghan government of President Hamid Karzai fight an insurgency by Taliban Islamists.