The corpses found at Tel Sharaf in Salaheddin province were "decomposing and had been strapped with explosive vests", said General Mezher al-Azzawi, a commander of operations in the area.

They included "the abductees who appeared in Daesh's last video", he added, using an Arabic acronym to refer to the jihadist group.

On Saturday, IS threatened to execute captives if Baghdad did not release Sunni Muslim women held in its prisons within three days.

In a video posted to the group's Amaq propaganda outlet, the jihadists displayed six men with badly bruised faces they said were Iraqi police or members of the Hashed al-Shaabi paramilitary force.

The corpses were transported to Tuz Khuramtu hospital south of Kirkuk, a Salaheddin policeman said.

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

It has 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 the former Soviet republics.