Gunmen broke into the home of the administrator for the Rashid area, south of Baghdad, killing one of his guards, an interior ministry official said.
They then moved to the nearby house of Captain Adnan al-Obaidi, a police officer in an anti-terrorism unit, and killed him, his wife and their two children, the official said.
A medical official confirmed the toll.
Gunmen also shot dead the imam of a Sunni mosque near the main southern port city of Basra, police and a Sunni endowment official said.
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Mohammed Khamis, the nephew of power tribal sheikh Ahmed Abu Risha, who is a key supporter of Sunni anti-government protesters in Anbar province and also led the uprising against Al-Qaeda in the province from 2007, confirmed that two members of his tribe were killed.
Hundreds of gunmen then gathered in the area of the Anbar Operations Command headquarters near Ramadi, the captain said.
The area is one of the main centres of the Sunni protest movement in Iraq, which began almost five months ago.
Demonstrators from Iraq's Sunni Arab minority accuse authorities of marginalising and targeting their community, including through wrongful detentions and accusations of involvement in terrorism.
While the government has made some concessions, such as freeing prisoners and raising the salaries of Sunni anti-Al-Qaeda fighters, underlying issues have not been addressed.