Six of the men had appeared in an ISIS video demanding that the government release female prisoners
Iraq forces find bodies of eight ISIS captives
Iraqi security forces have found the bodies of eight people kidnapped by ISIS, underlining the threat posed the extremist group six months after the government declared it defeated.
ISIS posted a video online on Saturday showing six captured members of Iraq's security forces and threatening to kill them within three days unless the government released female Sunni Arab prisoners.
The bodies were found at Tel Sharaf in Salaheddin province on Wednesday evening. They 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 said.
The identity of the other two victims was not clear.
The bodies were taken to Tuz Khurmatu hospital south of Kirkuk to prepare them for burial, a Salaheddin policeman said.
The ISIS video showed six men with badly bruised faces who their captors said were "either Iraqi police or members of the paramilitary forces, Hashed Al Shaabi".
Activists launched a "save my father" campaign on social media, asking the Iraqi government to act immediately to free the hostages.
Although Baghdad declared victory over ISIS in December, the extremist group continues to carry out deadly attacks in northern Iraq that are being attributed to its sleeper cells.
In response to the killings, influential MP Hamam Hamoudi, of the Islamic Supreme Council of Iraq, called for the retaliatory execution of ISIS prisoners being held in Iraqi government prisons.
Iraq has detained hundreds of people including women and children who have been identified as extremists or relatives of ISIS fighters.
The US Central Command strongly condemned the killings on Thursday.
"We join our Iraqi partners in mourning the brutal and senseless murder of these men, and together we remain steadfast in our commitment to destroy the remnants of Daesh," said General Paul Funk, commander of the Combined Joint Task Force - Operation Inherent Resolve.
"We will continue to work with our Iraqi partners to achieve the enduring defeat of the evil criminal organisation for the innocent civilians of Iraq, our nations, and all mankind."
Meanwhile, Iraq's parliament speaker Salim Al Jabouri said that the manual recount of contested votes in the May general election would begin next week.
The outgoing parliament this month passed a law to hold a nationwide manual recount, but the panel of judges now in charge of the recount said it would only be conducted only for problematic ballots.
Mr Al Jabouri said the parliament's term will end on Saturday unless MPs vote to extend it until after the recount is complete.