A car driven by a suicide bomber blew up next to the interior ministry in central Baghdad on Monday morning, causing a number of casualties, an official and AFP journalists said.
It was not immediately clear how many people were killed or wounded in the attack, which occurred at about 7:30 am (0430 GMT) in the Bab al-Sharji area. Ambulances could be heard rushing to the scene as helicopters flew overhead.
An interior ministry official, speaking on condition of anonymity, said the explosion was the work of a suicide car bomber. State broadcaster Al-Iraqiya TV also reported this as the cause of the attack.
The blast came after violence across Baghdad on Thursday killed 60 people.
Iraq is mired in a political row with authorities calling for the arrest of Sunni Vice President Tareq al-Hashemi on charges he ran a death squad, accusations Hashemi denies.
Prime Minister Nuri al-Maliki has also called for the sacking of his Sunni deputy Saleh al-Mutlak, who has denounced the premier as a dictator "worse than Saddam Hussein".
Meanwhile, the Sunni-backed Iraqiya bloc of Hashemi and Mutlak has boycotted cabinet and parliament.