The dead included a couple and two daughters, and two brothers of the husband, according to a police officer in Tarmiyah, 30 miles north of the capital. The throats of two women were slit, while the other four people were shot execution-style; two of the couple's other children were not harmed.
A motive for the attack was not immediately clear. The Tarmiyah officer and a police investigator said the Sunni Arab victims were not affiliated with Sunni militiamen, many of them former insurgents, who joined U.S. forces and turned against Al Qaeda in Iraq.
The police officials spoke on condition of anonymity because they were not authorized to speak to the media. The officer said the three male victims were working as shepherds on a farm near their house.
Further north, in the city of Mosul, Iraqi forces assisted by American advisers detained 18 suspected associates of Al Qaeda in Iraq during searches of residential buildings, the U.S. military said. Insurgents retain a foothold in Mosul despite blows to their networks that have sharply reduced violence nationwide.
Also Wednesday, a double bombing injured 25 civilians in the Shiite holy city of Karbala ahead of an Islamic holiday, officials said.
One bomb first exploded in a restaurant, drawing onlookers and police, before a suicide bomber on a motorcycle then drove toward the crowd and detonated his explosives, said a provincial police officer and a doctor at al-Hussein General Hospital.
The officials spoke on condition of anonymity because they were not authorized to speak to the media.
The Karbala restaurant was strewn with overturned tables and chairs in the aftermath of the blasts. Fragments of broken dishes and slippers littered the bloodstained floor.
"Where is the protection, where is the government?" a distraught woman shouted at Iraqi troops who arrived at the scene.
Karbala, home to important Shiite shrines, has periodically been targeted by Sunni militants. The holiday of Eid al-Adha, or Feast of Sacrifice, begins for Iraq's Sunnis on Friday, while Shiites start the celebrations on Saturday.