The Taliban infiltrator then stole their weapons and fled the police outpost in the Chinarto district of Uruzgan province, authorities said, triggering a manhunt.
The attack just after midnight is part of the Taliban’s unprecedented winter campaign of nationwide violence despite a renewed international push to restart formal peace talks.
“Our investigation shows that this policeman collaborated with the Taliban, drugged his colleagues and killed them when they were unconscious,” Dost Mohammad Nayab, the spokesman for Uruzgan’s governor, told AFP.
Deputy provincial police chief Rahimullah Khan confirmed the account and said an operation had been launched to track down the killer.
Taliban spokesman Zabihullah Mujahid, giving a different account, said nine policemen were killed after the militants captured the police outpost in Chinarto.
“Our mujahideen seized several weapons including AK-47s, machine guns and rocket-propelled grenades,” Mujahid said.
So-called insider attacks — when Afghan soldiers or police turn their guns on their colleagues or on international troops — have been a major problem during NATO’s long years fighting alongside Afghan forces.
On January 17 nine Afghan policemen were shot dead in Uruzgan by four rogue colleagues said to be Taliban infiltrators.
The Afghan military, which has been built from scratch since the fall of the Taliban regime in 2001, has struggled with insider attack killings, high casualty rates and mass desertions.
Stretched on multiple fronts as the insurgency expands, Afghan forces have largely fought the ascendant Taliban on their own since NATO’s combat mission formally ended in December 2014.
In recent months the Taliban briefly captured the northern city of Kunduz, the first urban centre to fall to them in 14 years of war, and have seized territory in the opium-growing southern province of Helmand.
The uptick in violence comes amid renewed international efforts to revive peace talks with the Taliban, which are locked in a tussle for supporters with the Islamic State group.
Delegates from Afghanistan, Pakistan, China and the United States convened in the Afghan capital last week for a one-day meeting seeking a negotiated end to the 14-year Taliban insurgency.
The first round of the so-called “roadmap” talks was held in Islamabad earlier this month as the four nations try to lay the groundwork for direct dialogue between Kabul and the Islamist group.
Taliban representatives were notably absent in both rounds and analysts caution that any substantive talks are still a long way off.
The Taliban have stepped up attacks on government and foreign targets in Afghanistan this winter, when fighting usually abates, underscoring a worsening security situation.
Observers say the intensifying insurgency highlights a push by the militants to seize more territory in an attempt to wrangle greater concessions when the talks formally start.