"Our security and military forces will take forceful revenge against these terrorist cells," he told senior military officials and ministers at a meeting in Baghdad.

"We promise that we will kill or arrest those who committed this crime," he added.

The corpses, found Wednesday at Tel Sharaf in Salaheddin province, were decomposing and had been strapped with explosive vests, the army said.

They included six abductees who had appeared in an IS video with badly bruised faces. IS claimed they were Iraqi police officers or members of the Hashed al-Shaabi paramilitary force.

In the video posted Saturday by the Amaq propaganda outlet of IS, the jihadists threatened to execute their captives unless Baghdad released Sunni Muslim women held in its prisons within three days.

But Abadi said that autopsies indicated the captives were already dead when the video was posted.

Iraq declared victory over IS in December after expelling the jihadists from all urban centres including second city Mosul in a vast military campaign.

Authorities have detained hundreds of women and children identified as jihadists or related to suspected IS fighters, and has put many on trial.

More than 300 people -- including some 100 foreign women -- have been sentenced to death in Iraq for joining IS, while similar numbers have been handed life terms, judicial sources say.

Most of the convicted women are Turkish or from former Soviet republics.