The victims were described as former "Sahwa elements" -- members of the Sons of Iraq -- a Sunni coalition united to provide security to their community in al-Mishahida village. the source said.
"Unidentified gunmen [assuming] the [identify] of policemen stormed into some residence[s] of the villages of al-Mishahida area 25 miles to the north of Baghdad where they kidnapped eight former Sahwa elements and killed them," the source told the news website.
"The gunmen executed the Sahwa elements in one of the orchards by guns and left them after managing to escape where the police forces conducted a search operation to net the gunmen and the corpses were transported to the morgue," the source said.
In other attacks across Iraq, at least 14 people were killed and 26 injured Sunday, Xinhua reported.
Ten people -- mostly teenagers -- died and 24 were injured when an improvised explosive device detonated near a soccer field in the Nahrawan district in eastern Baghdad, an Interior Ministry source told Xinhua.
A roadside bomb in the Algeria area in eastern Mosul killed a civilian and injured his brother, a police source said.
Unidentified gunmen killed one employee when they attacked a power station in the al-Arbajiah area in eastern Mosul, and an attack at a checkpoint resulted in the death of a soldier in the al-Najjar area in western Mosul, the report said.
A sticky bomb placed in a car in the Jamiah district of Hilla resulted in the death of the driver of the vehicle and the injury of another person, police said.