A suicide bomber blew up a fuel truck outside a police centre in the Iraqi city of Mosul on Thursday, killing 11 people, and rebels fired mortar rounds at another station in coordinated attacks, police and doctors said.
The blast, heard across Mosul, a flashpoint of insurgents north of Baghdad, left nine charred bodies and wounded 26 people, police said.
Shortly after the explosion, insurgents fired mortar shells at another police centre and clashed with police. Nine more people were killed in the violence.
Another police source said a car bomb, also driven by a suicide bomber, could have exploded before the suicide truck bomb.
The governor imposed a curfew and Iraqi forces were patrolling the city, an agency reporter in Mosul said.
Mosul, Iraq's third largest city, has witnessed a recent escalation of violence by Sunni insurgents and between Sunni Arabs and ethnic Kurds vying to control the urban area and the surrounding area.
Last month, a car bomb followed by a suicide attacker strapped with an explosive vest killed 18 people and wounded 11 near a passing Iraqi army and police patrol in a town near Mosul.
In November 2004, the entire police force in Mosul disintegrated after an insurgent offensive. It was rebuilt with the help of the US military.
Sunni Arab insurgents battling US troops and the Shi'ite-led government in Baghdad frequently attack Iraq's security forces.
Building Iraq's police and army is a key part of Washington's plan for an eventual pullout of its troops.