At least 15 people have been killed in a series of bomb blasts across Iraq, police and medics say.

Wednesday's attacks follow a sharp increase in violence that has prompted warnings of a full-blown sectarian conflict between Sunnis and Shia.

A suicide bomber wearing an explosives vest detonated himself in the midst of a group of government-backed Sunni fighters who were collecting their salaries east of the city of Fallujah, killing six, police sources said.

In Baiji, 180km north of the capital Baghdad, police said a roadside bomb killed four policemen.

A car bomb in a Shia district in northeastern Baghdad killed at least three people and wounded 14, police and hospital sources said.

Another car bomb north of the city of Ramadi killed two policemen and wounded another 10.

Iraq is home to a number of Sunni groups including a local al-Qaeda affiliate that has launched frequent attacks to undermine the government and provoke wider confrontation.

Violence in Iraq has increased as the civil war in neighbouring Syria puts a strain on fragile relations between Sunni and Shia Muslims.

Though still well below its height in 2006-07, provisional figures from rights group Iraq Body Count indicate the number of violent deaths in April was the highest monthly toll since 2009.

Source: Agencies