All of the corpses had gunshots to the head and chest, and were found abandoned in farmland near the town of Tarmiyah, two police officers and a medical source said.
The dead included two tribal chiefs, four policemen and an army major.
The kidnappers, wearing military uniform and travelling in what appeared to be army vehicles, had told the victims' families that they were suspects in a variety of investigations and had to be taken away for questioning.