A suicide bomber blew himself up near a group of anti-Qaeda fighters as they were receiving salaries north of Baghdad on Monday, killing 22 people, the second bloody attack to hit Iraq in as many days.
The blast, which also wounded at least 44 people, came soon after officials raised the salaries of the Sunni militiamen in a bid to placate weeks of anti-government demonstrations in mostly-Sunni areas of the country.
It also comes just a day after a coordinated assault on a police headquarters in a disputed city in the north killed 30 people amid a spike in violence nationwide.
The attacker struck at 11:00 am (0800 GMT) in Taji, which lies 25 kilometres (15 miles) north of Baghdad, as the fighters were collecting their salaries.
In total, 22 people were killed, the vast majority of them militiamen but also two soldiers, according to a security official and a medical source. At least 44 others were wounded, among them eight soldiers.
Members of the Sahwa, otherwise known as the Awakening Councils or Sons of Iraq, are made up of a collection of Sunni tribal militias that sided with the US military against Al-Qaeda from late-2006 onwards, helping turn the tide of Iraq's bloody insurgency.
They are often targeted by Sunni militants linked to Al-Qaeda who regard them as traitors.
Violence was also reported in the capital and in the ethnically-mixed northern city of Kirkuk.
In Baghdad, a roadside bomb killed a police officer and wounded three of his colleagues, while four people were shot dead overnight in Kirkuk, officials said.
The latest unrest came a day after a coordinated attack on Kirkuk's police headquarters -- a suicide car bomb followed by an assault by grenade-throwing gunmen -- killed 30 people and wounded 88 others.
The violence comes as Iraq grapples with a political crisis pitting Prime Minister Nuri al-Maliki against his government partners amid weeks of protests calling for him to resign.
No one has claimed responsibility for the spate of attacks but local security officials blame Al-Qaeda's front group in Iraq, which often targets security forces and officials in a bid to destabilise the country and push it back towards the sectarian bloodshed of 2005 to 2008.
Kirkuk, an ethnically mixed city 240 kilometres (150 miles) north of Baghdad, lies at the heart of a swathe of disputed territory claimed by both the central government and Iraq's autonomous northern Kurdish region.
The unresolved row is persistently cited by diplomats and officials as the biggest threat to Iraq's long-term stability.
The violence was the latest in a spike in unrest that saw 246 people killed last month, the most since September, according to an AFP tally.