Insurgents frequently attack members of the Sunni militia, also known as Sahwa, which joined forces with US troops at the height of the Iraq war to fight al-Qaida.
In one of today's attacks, gunmen opened fire from a speeding car, targeting a security checkpoint manned by anti-al-Qaida Sunni fighters near the town of Balad, 80 kilometers north of Baghdad. Three Sunni fighters were killed and four were wounded in that attack, police officials said.
Medical officials confirmed the casualty figures. All officials spoke on condition of anonymity as they were not authorised to talk to media.
Also today, in a statement posted on a militant website, the Islamic State of Iraq and the Levant said it had carried out attacks in the Iraqi capital the day before in retaliation for the military operations against the city of Fallujah in western Anbar province. Fallujah has been in the hands of the Islamic State and other Sunni insurgents since last December.
"We tell the spiteful Shiites and their government... that our lions are craving the taste of your flesh and blood," it said.
Iraq has seen a spike in violence since April 2013, with the death toll climbing to its highest levels since the worst of the country's sectarian bloodletting in 2006-2008. The United Nations says violence killed 8,868 people in 2013.