Iraqi officials say at least 20 people have been killed after gunmen wearing military uniforms and explosive belts stormed into the provincial council headquarters in Tikrit.
Investigators say a car exploded outside of the building on Tuesday shortly after the gunmen forced their way inside. Authorities say the attackers have been hurling grenades at law enforcement officers.
Officials say about 60 people have been wounded.
There are conflicting reports on whether the attackers are holding hostages. The Associated Press quotes the provincial governor as saying he has lost contact with three lawmakers who were inside.
Police have imposed a curfew in Tikrit, which is about 140 kilometers north of Baghdad. Tikrit is the hometown of the late Iraqi dictator Saddam Hussein.