The officers, part of a US-sponsored community force known as the Afghan Local Police (ALP), were patrolling in Nad Ali, a restive town in the province of Helmand when hit by the blast, the official said.

"It was a roadside bombing. It hit a local police vehicle and killed six policemen. The bomb was planted by the Taliban," Mohammad Ibrahim, the Nad Ali district chief, told AFP.

He said the bombing was in retaliation for recent operations by the ALP against insurgents.