At least nine people were killed and another 23 wounded on Saturday when a suicide bomber struck the headquarters of a US-allied Sunni militia south of Baghdad, an Iraqi army officer said.
The bomber detonated his payload as an Iraqi army contingent was visiting the headquarters of the local Sahwa "Awakening" movement to pay salaries, Lieutenant Haidar al-Lami told AFP.
He added that the killed and wounded included Sahwas and soldiers.
The Sahwas, former Sunni insurgents who allied with US forces beginning in 2006 to drive out Al-Qaeda in Iraq, have played a crucial role in improving security in the war-battered country.
The attack took place in the town of Latifiyah, in a religiously mixed part of Babel province once known as the "Triangle of Death" that saw scores of attacks in the years after the March 2003 US-led invasion.
The attack came amid an upturn in violence over the past week that saw a series of bombings in Baghdad and a suicide truck bomb in the northern city of Mosul Friday that killed five US soldiers and three Iraqi security forces.
The Mosul bombing was the deadliest attack on US forces in more than a year and underscored the lingering insecurity in some areas of the country. The US military views Mosul as the last urban bastion of Al-Qaeda in Iraq.
The city -- Iraq's second largest -- has remained dangerous despite repeated US and Iraqi operations over the past several months, both because of ethnic divisions between its Sunni Arab and Kurdish residents and tribal rivalries.
In recent weeks, the US military has played down talk of a rise in violence, as its soldiers prepare to withdraw from Iraqi cities and major towns by June 30 and from the entire country by the end of 2011.
Security has improved dramatically since 2007 when Iraqi and US forces launched offensives against Al-Qaeda with the help of the Sahwas, who were trained by the US military but are now mostly funded by the Iraqi government.
But insurgents are still able to strike with deadly results. A total of 252 Iraqis were killed in violence in March, almost the same tally as the previous month but up from January, when 191 Iraqis died in unrest.
The attacks in Baghdad on Monday, Tuesday and Wednesday killed at least 49 people and wounded 182.