Up to 25 people have been killed after a group of men dressed in Iraqi army uniforms stormed three houses in southern Baghdad, Iraqi authorities have said.
The attack took place in a village in the capital's Rasheed district in the early hours of Saturday.
"Men wearing uniforms and driving vehicles similar to those used by the army stormed three houses in the village of Sufiya ... and killed 25 people, including five women," an interior ministry official said.
The victims were handcuffed and shot in the head, police said.
Major General Qassim al-Moussawi, a Baghdad security spokesman, said some of the victims were members of the Iraqi security forces and others of the Awakening Councils, Sunni militias who have allied with US forces to fight al-Qaeda.
He said authorities had arrested 25 people and sealed off the area to conduct a search for other suspects.
Seven people were left alive with their hands tied behind their backs after the attack, he said.
Al Jazeera's Zeina Khodr, reporting from Baghdad, said the Rasheed district used to be an an al-Qaeda stronghold until the Awakening Council clamped down on the fighters.
"[Awakening Council members] are targets, just like security officials government officials."
She said the attack came in a time of political uncertainty with no clear winner emerged from the March 7 national elections and the political parties still negotiating to form alliances.
"A lot of discussion has taken place but still no progress. So, a lot of tension and speculation that the post-election period might see an upsurge in violence.
"It could be the Iraqi style of negotiating. This is what you hear when you talk to people here. They are expecting violence, maybe to step up pressure."