Militants detonated a pick-up truck full of explosives next to a police convoy as it drove northwest of Baghdad on Saturday, killing five policemen.
Police said five other officers and nine civilians were wounded in the bombing in Garma, 30 km from the capital.
The attack in an area once dominated by al Qaeda and other Sunni Islamist militants took place a week before provincial elections seen as a key test of security gains after years of sectarian slaughter that followed the 2003 US-led invasion.
Militants continue to stage attacks despite a sharp fall in overall violence in the last 18 months. US officials have warned of a possible uptick in violence before the vote on 31 January.