An Afghan police officer and cook poisoned their colleagues at a checkpoint in an assault co-ordinated with rebel fighters which left six dead in the country's south, officials say.
It was the latest in a string of attacks from inside the Afghan army and police that are threatening to undermine both the partnership with international troops - which have been the target of many attacks - and the morale of Afghan forces, who have suffered equally heavy casualties from such strikes.
The police officer and the cook worked with outside insurgents in the assault, which hit police manning a checkpoint in the Gereskh district of Helmand province, the governor's office said in a statement.
They poisoned two of the officers and then the militants attacked from outside, killing the remaining four officers, provincial spokesman Ahmad Zirak said. He did not say how the officers were poisoned.
The police officer was captured as he fled, but the cook escaped and remains at large, Mr Zirak added.
The insurgent gunmen escaped by motorcycle with weapons and ammunition, the governor's statement said.
A recent upsurge in the number of insider attacks on coalition troops by Afghan soldiers or police - or insurgents disguised in their uniforms - has further undermined public support for the war in the West. So far this year, at least 52 foreign troops - about half of them Americans - have been killed in insider attacks.
The Afghan government has not provided statistics on the number of its forces killed in insider attacks. However, US military statistics show at least 53 members of the Afghan security forces had been killed by the end of August.
Meanwhile, a Taliban attack elsewhere in Helmand killed two district community council members, while Taliban-fired rocket-propelled grenades destroyed a warehouse full of food destined for the main US base in Afghanistan.
Insurgents ambushed the council members while they were driving to a tribal meeting in the volatile Sangin district, the governor's office said in its statement, adding that the attackers escaped and police are pursuing them.