The gunman opened fire with his assault rifle after waking up at 3 a.m. ostensibly to take over guard duty at a small command post in Paktika province, killing everybody inside, including the commander, according to officials. He then took their weapons, piled them in a pickup truck and sped away.
It was the latest in a growing number of attacks by Afghan security forces against their own people or against international troops in Afghanistan in recent years, some the result of arguments and others by insurgent infiltrators.
Provincial police chief Dawlat Khan Zadran said the incident took place in Yayakhil town of Yayakhil district.
Bowal Khan, chief of Yayakhil district, identified the gunman as Asadullah and said he goes by one name, as do many Afghans.
Khan said his own brother was among those killed, along with the commander of the post, identified as Mohammad Ramazan, and two of the commander's sons.
The motive for the killing was not known, but police in the area blamed the Taliban for the attack. Paktika is a stronghold of the Haqqani network, a Pakistani-based group with ties to the Taliban and al-Qaida. Although they mostly attack U.S.-led coalition forces, they have often carried out assaults and bombings against the Afghan army and police.
Taliban spokesman Zabiullah Mujahid claimed responsibility for the attack and said the shooter was a member of the insurgent group. He added in a text message that he took the dead police officers weapons and handed them over to the Taliban.
"This man is a coward. What he did is part of the Taliban conspiracy," Khan said.
Khan and Zadran said the killer's two brothers were being held for questioning.
The increasing number of attacks by Afghan police and soldiers has cast doubt on the readiness of Afghan security forces to take over their own security as the U.S.-led international coalition prepares to end its combat mission by the end of 2014.
So far this year, 16 NATO service members have been shot and killed by Afghan soldiers and policemen or militants disguised in their uniforms, according to an Associated Press tally. That equals 18 percent of the 84 foreign troops killed this year in Afghanistan. Of the approximately 80 NATO service members killed since 2007 by Afghan security forces, more than 75 percent were in the past two years.
There also have been recent examples of Afghans killing their own comrades.
A member of a village-level force that provides security in areas where the Afghan army and police cannot was accused of involvement in the killing of nine members of his unit in March in southern Uruzgan province. They also were shot and killed while asleep at their post in the village of Oshi in the province's Charchino district. It remains unclear if he killed them or allowed a killer into the post, but he was never apprehended.
The village units known as Afghan Village Police, or by their Afghan acronym ALP, are trained by the U.S. but commanded and run by the Afghan government and police.
Taliban infiltration of the ALP is considered more difficult as all their members are recruited locally and vetted by village elders before joining, so they usually know each other.
In other violence Friday, a motorcycle bomb parked by the side of a road exploded, killing an Afghan police officer and wounding another in Sangin district of southwest Helmand province, police said. They added that another police officer was shot and killed late Thursday outside his house in the capital of Helmand.
NATO also said Friday that two of its service members were killed in southern Afghanistan — one died in a roadside bomb explosion on Friday and the other one in an insurgent attack on Thursday. NATO did not disclose any other details.
So far this year, 88 international troops have been killed in Afghanistan.