Gunmen armed with silenced weapons attacked a house in east Baghdad on Tuesday, killing a man, his wife and four children, a security official and a medic said.
The attack took place in the Zayouna area, an interior ministry official said, adding that the motive for the crime was not known.
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Gunmen who were also armed with silenced weapons carried out a similar attack on November 28 in Tarmiyah, 45 kilometres (28 miles) north of Baghdad, killing seven members of the same family.
In that case, two members of the family, including one of those killed, belonged to the anti-Qaeda Sahwa militia force, made up of Sunni tribesmen who fought the militant group and helped turn the tide of the war in Iraq.
Also on Tuesday, a roadside bomb wounded three police in the restive north Iraq city of Mosul, a police officer and a doctor said.
Violence in Iraq has decreased dramatically from its peak in 2006 and 2007, when brutal sectarian violence swept the country, but attacks remain common.