A suicide bomber attacked a government-backed militia north of Baghdad on Monday, killing at least 19 people in an apparent attempt by Sunni insurgents to stoke unrest against Iraq's Shiite prime minister, Nouri al-Maliki.
Police said the bomber had infiltrated a meeting of Sahwa tribal fighters and detonated his explosives as they were gathering to pick up salaries in Taji, a town 20 km (12 miles) north of the capital.
The seventh suicide bombing in a month was part of an surge in violence a year after US troops pulled out of the OPEC oil producer, where Shiite, Sunni and ethnic Kurdish factions still struggle over how to share power.
"We got a call they had been a huge blast on the Sahwa headquarters in Taji. The Sahwa were there to collect their pay," said local police commissioner Furat Faleh. "When we rushed to the hall ... people were lying bleeding all around and cash was scattered in pools of blood."
The Sahwa or "Sons of Iraq" are former Sunni insurgents who rebelled against Al Qaeda in the Sunni heartland province of Anbar at the height of the US-led war and helped American troops to turn the tide of the conflict.
No group claimed responsibility for Monday's attack, but Al Qaeda's affiliate, Islamic State of Iraq, has vowed to take back ground lost to American and US forces, and has urged Iraqi Sunnis to rise up against Mr. Maliki's government.
A suicide bomber and gunmen killed at least 33 people in a huge blast at the police headquarters in the disputed northern oil city of Kirkuk on Sunday.
Maliki has been struggling to end mass protests by Sunni Muslims against what they see as marginalization of their sect since the fall of Saddam Hussein and the rise of Iraq's Shiite majority.
The Sunni unrest and the violence are compounding fears that the war in neighbouring Syria – where Sunni rebels are battling to topple President Bashar al-Assad, an ally of Shiite Iran – could undermine Iraq's own delicate sectarian and ethnic balance.