A suicide bomber has killed at least nine people and injured 29 more southwest of Baghdad, Iraqi police says.

The bomber attacked government-backed Sunni militia members lining up to be paid, in the town of Radwaniya.

The Sunni militia fighters, known as Sahwa or Sons of Iraq, were once allied with al-Qaeda, but turned against the militant group in 2006.

Among the wounded were at least two soldiers, the Interior Ministry said.

Sahwa members have been frequently targeted by militants since they joined the US military and government forces in the fight against al-Qaeda.

The blast occurred as a political vacuum continued following elections in March.