KABUL (AFP) - Militants in north-east Afghanistan killed 18 police in an ambush, the interior ministry said on Friday, as the nation's security forces struggle to thwart the Taleban with decreasing assistance from international troops.

The police convoy was caught in a firefight in the remote province of Badakhshan on Wednesday when they were returning from an anti-insurgent operation.

"The acting interior minister is deeply saddened about the killing of 18 policemen and wounding of 13 others in a terrorist attack in Warduj district of Badakhshan," a statement from the interior ministry said.

"A group of Afghan police forces on their return from a clean-up operation on the outskirts of Warduj district faced an enemy ambush and it resulted in the killing of brave Afghan policemen."

The mountainous north-east of Afghanistan is far from the Taleban heartlands of the south and is relatively peaceful.

But Taleban militants killed 17 captured Afghan soldiers in the same district in March. The men were taken hostage while guarding a convoy.