Hundreds gathered in villages north of Baghdad at the weekend, to bury the victims of an ISIS attack that killed six members of the same family.
The people killed in the attack on Friday included two women, as well as a lawyer and a police officer in the village of Al Bobdor, 133km north of the Iraqi capital.
Witnesses said men in military uniform had carried out the three attacks on the victims' homes in the village.
The Iraqi military said it was a revenge attack ordered by a village resident who had been driven out by neighbours who accused him of being an ISIS member.
It said the perpetrators entered the area on foot, wearing military fatigues as a disguise, and entered the homes on the pretext of search operations before carrying out the murders.
An ISIS statement said those killed on Friday had been spying for the Hashed Al Shaabi or Popular Mobilisation Forces, a largely Shiite-led coalition of paramilitary forces that played a key role in 2017 in ending the militants' control of large parts of Iraqi territory.
Many Popular Mobilisation Forces units are funded and trained by Iran and the government retains only nominal control.
Ali Al Bayati, of the semi-official Independent Human Rights Commission, said the killings showed clear security loopholes.
Iraq declared ISIS territorially defeated in December 2017 after a three-year fight aided by US-led coalition air strikes.
ISIS attacks in urban areas have since dramatically dropped, but Iraqi troops continue to battle sleeper cells in the country's mountainous and desert areas.
