At around 8.30am (0430 GMT) on Thursday fighters drove up to the police station, 75km from Baghdad, and opened fire at officers outside the building, said a police colonel at the scene on condition of anonymity.
Four of the fighters were shot dead, the colonel said.
Minutes later, five policemen were killed when a minibus hurtled towards the building and the driver blew up the vehicle, he added.
He said 18 policemen were among at least 21 wounded.
Meanwhile, at least one man was killed and a car destroyed when a mortar round landed on the road linking al-Adhamiya and al-Mansour neighbourhood to the west of Baghdad, reported our correspondent.
Other explosions were heard in different places in the Iraqi capital in the early hours of Thursday.
US-backed Iraqi police are frequent targets of attacks in the country.
On 28 July, a massive bombing outside a police station in the flashpoint city of Baquba, north of Baghdad, killed 70 people, many of them jobseekers looking to join the fledgling security force.