Grenade attacks are relatively uncommon in Afghanistan but it was the second time in less than 48 hours that police have been targeted in such a way.

The attacker threw at least two grenades at a police pickup truck in a crowded market in Khost city before fleeing the area, Khost provincial police spokesman Mir Akbar Mangal told AFP.

"Twenty people, including several police, were wounded in the attack. No one has been killed," he said, adding that police were hunting the attacker.

There was no immediate claim of responsibility, but the Taliban have said they were behind a grenade attack on a police station in Kabul on Friday night.

Police said nobody was injured after a man lobbed at least one grenade at a district police station in the west of the capital.

The insurgents who have been fighting NATO-led foreign troops and Afghan government forces for a decade use roadside and suicide bombs more frequently than grenades.