The Islamic State group said it has killed eight men in Iraq's Salahuddin province north of Baghdad for allegedly cooperating with the government security forces and international airstrikes targeting the group.

A collection of photos posted late Monday on a Twitter account frequently used by the militants showed eight bearded men in orange jumpsuits with their hands tied behind their backs. Five were identified as police officers and two as informants, but no information was provided on the eighth victim.

The photos showed the blindfolded men being brought to a riverbank by masked gunmen under what looks like a bridge, then lined up on their knees and shot in the head. The group didn't mention when the killings took place.

A provincial official, who spoke on condition of anonymity for his safety, offered a different account; he said Tuesday that the men were army officers who abandoned the army before the militants took over parts of the province last year and that they didn't cooperate with the Iraqi government forces.

The Salahuddin provincial capital, Tikrit, and other nearby towns have been in militant hands since June when the Islamic State group expanded with lightning speed across Sunni-dominated regions of northern and western Iraq as government forces collapsed.

Since then, the militant group has declared a self-styled caliphate over about a third of Iraq and neighboring Syria. But there has been growing resentment among some residents fueled by the group's enforcement of its extremist interpretation of Islamic law, economic stagnation and a lack of public services.

Seeking to squash any potential uprising, the militants have begun killing policemen and soldiers living in areas of Iraq under their control — especially after the U.S.-led coalition air campaign began supporting ground offensives by Iraqi government forces, Kurdish fighters and Shiite militias.