A suicide bomber has killed at least 43 people and injured 40 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 Awakening Councils, 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.
"There were more than 85 people lined up in three lines at the main gate of the military base to receive salaries when a person approached us", a survivor, 20-year-old Tayseer Mehsen, told the Reuters news agency at Mahmudiya hospital.
"When one of the soldiers tried to stop him, he blew himself up."
The Sahwa are credited with helping to reduce the overall levels of violence in Iraq since they joined the US military and government forces in the fight against al-Qaeda.
Control of the Sahwa passed from the US military to Iraq in October 2008, and since then their wages, said to have been cut considerably, have been paid by the government in Baghdad.
But the Sahwa have been frequently targeted by militants and have recently complained about harassment from government troops as a political vacuum continues following inconclusive elections in March.
Sunni insurgents have sought to exploit the deadlock created by a failure of Sunni, Shia and Kurdish factions to agree on a new coalition government.
There are also fears that the political uncertainty could hinder the planned withdrawal of all US combat troops from Iraq by the end of August, in preparation for a full military departure by 2012.