IS extremists murder Iraqi police officer 2 weeks after kidnapping him
The militant group had released photos purporting to show the decapitated body of Colonel Yasser al-Jourani, whom they had seized while he was hunting with friends in Iraq's Hamrin region earlier this month.
One of his hunting companions was found shot dead, while a second who had been tortured later died of his wounds, a security source told AFP.
The spokesman of Iraq's armed forces chief said Prime Minister Mustafa al-Kadhimi had ordered that security efforts against IS forces be boosted.
"We will pursue the terrorists to achieve justice and vengeance for our martyrs," the army chief's spokesman said.
A low-level IS insurgency continues to disrupt efforts to restore stability to Iraq, which is scarred by years of warfare and unrest.
Over the past few days security forces announced a large-scale operation in the mountainous Hamrin region.
Iraqi military operations and airstrikes killed "five Daesh agents", an Arabic acronym for IS, leading to the discovery of several "terrorist caches" containing bombs and weapons, a statement from Iraq's security forces read.
"Two bodies of two kidnapped people were found," it added, without naming the victims.
IS overran large swathes of northern and western Iraq in a lighting offensive in 2014 before eventually succumbing to counter-attacks by government forces backed by a US-led coalition in 2017.
Today, IS maintains a largely clandestine presence in Iraq and Syria and conducts a sustained insurgency on both sides of the border, according to a United Nations report published early this year.
Across the two countries, IS is believed to retain about 10,000 active fighters, according to the report.
The last major attack claimed by IS in Iraq targeted a market in Baghdad's Shia neighbourhood of Sadr City in July and killed about 30 people.