The party had opened its regional office only recently, and the blast, which happened before dawn, injured no one.

The attack on the party's offices followed Saturday's bombing near a Sunni mosque in Hilla that wounded two worshippers at dawn prayers. One of the wounded was a member of a Sunni, government-allied Sahwa, or 'Awakening' militia.

No one immediately claimed responsibility for Saturday's and Sunday's attacks against Sunni targets.

On Friday, five consecutive bombings targeted Shia mosques in Baghdad, most of them connected to the movement of firebrand cleric Moqtada al-Sadr.

At least 30 people were killed in those attacks and at least 100 others wounded, police said.