A suicide bomber blew himself up near a group of anti-Qaeda fighters receiving salaries north of Baghdad on Monday, killing 23 people, the second bloody attack to hit Iraq in as many days.

The blast, which officials said also wounded at least 44 people, came after Baghdad raised the salaries of the mostly-Sunni militiamen in a bid to placate weeks of anti-government demonstrations in predominantly-Sunni areas of Iraq.

The victims of Monday's attack, however, included both Shiite and Sunni anti-Qaeda fighters, an AFP reporter at the scene said.

The attack also comes a day after a coordinated assault on a police headquarters in a disputed city in north Iraq killed 30 people amid a spike in violence nationwide.

The bomber struck at 11:00 am (0800 GMT) in Taji, a town 25 kilometres (15 miles) north of Baghdad, as the anti-Qaeda fighters were collecting their salaries.

At least 23 people were killed, a vast majority of them militiamen but also three soldiers, according to a security official and a medical source. Another 44 were wounded, among them eight soldiers.

"It's a very awful and ugly attack," Raad Faisal Abbas, the town mayor, told AFP from the local hospital. "The victims are all young men, just trying to do a good job for their country."

One of the wounded, Ali Khalaf, said many of the victims died because security forces did not immediately approach the scene as they were afraid of a second explosion.

"I blame the army," said the fighter, who suffered burns all over his body.

"Normally, when we go (to collect our salaries), the army lets us enter the compound. This time, they left us outside and they blocked the entrance," he said.

"In the meantime, when we were gathering, the attack happened."

Soldiers blocked off access to the site of the attack, and barred journalists from getting to the scene.

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.

Sahwa fighters are often targeted by Sunni militants linked to Al-Qaeda who regard them as traitors.

Violence was also reported on Monday in Baghdad 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, located 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 2012, according to an AFP tally.