A car bomb set off by a suicide attacker and followed by gunmen storming a police headquarters in the north Iraqi city of Kirkuk, killed 30 people and wounded 70 others on Sunday, a police general said.
Militants had apparently sought to take control of the compound, but were unsuccessful, Brigadier General Natah Mohammed Sabr, the head of the city's emergency services department said.
The attackers struck at morning rush hour in the city centre, Sabr said, with the militants armed with guns, grenades and suicide vests looking to force their way into the police headquarters in the chaotic aftermath of the car bombing.
In addition to the casualties, the attack caused massive damage to nearby buildings, Sabr said.
No group immediately claimed responsibility for Sunday's coordinated attack, but Sunni militants including Al-Qaeda's front group in Iraq frequently target security forces and government land marks in a bid to destabilize the country.
Kirkuk lies at the heart of a swathe of disputed territory claimed by both the central government and Iraq's autonomous northern Kurdish region.
The unresolved row is persistently cited by diplomats and officials as the biggest threat to Iraq's long-term stability.
Militants often exploit a lack of coordination between the two sides' security forces and launch deadly attacks in the city, which remains one of the most violent in Iraq, and also in nearby towns.
The deadly violence shattered a relative calm in Iraq in recent days.
Baghdad has been grappling with a political crisis that has pitted Prime Minister Nuri al-Maliki against his former government partners amid weeks of protests calling for him to resign.