At least nine policemen were killed and two others wounded in an attack with mortars and automatic weapons on a federal police checkpoint in northern Iraq.
The attack in the town of Shurra, south of Mosul, on Wednesday was followed by a roadside bomb explosion as emergency personnel rushed to the scene, wounding another two people, medical sources said.
There were no casualties among the attackers, security officers said.
Mosul, 360km northwest of Baghdad, has been one of Iraq's major flashpoints in the recent wave of violence.
In a separate incident, unknown assailants killed a soldier in Mosul, while armed men killed a man in Baquba, a city north of Baghdad.
Prisoner transport attacked
On a highway in Anbar province, west of Baghdad, fighters in vehicles mounted with machineguns attacked an army checkpoint and a joint army-police convoy in an apparent attempt to free a captured senior al-Qaeda member who was being carried in the convoy.
The attack left four of the fighters dead, while a soldier and an attacker were wounded.
The violence comes a day after an al-Qaeda front group claimed brazen assaults on two prisons in Iraq that killed more than 40 people.
Security forces are hunting the prisoners who escaped during the assaults, to prevent them carrying out further attacks.
With the latest unrest, more than 650 people have been killed so far in July, making it the deadliest month in a year.