Massud Barzani, the president of Iraq's autonomous Kurdish region, vowed on Saturday to avenge three peshmerga fighters beheaded by the Islamic State jihadist group.
"We promise the families of these martyrs that their blood will not be wasted and that we will avenge them," Barzani said in an online statement.
"Those who martyr the peshmerga in this way, before, now and in the future, will see how the hand of the heroic peshmerga will reach them," he said.
A video showing IS jihadists beheading three members of the peshmerga security forces was posted online earlier this week.
It began with images of people being brought to a hospital and a voiceover saying that they had been wounded by peshmerga rocket fire.
Three prisoners wearing orange jumpsuits with their hands bound were later shown kneeling one at a time, with masked militants standing guard, at locations said to have been hit by peshmerga fire.
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They were then beheaded.
One militant addressed Barzani directly in the video, saying that with "every rocket you launch against the Muslims... you will kill one of your prisoners with your hands".
The White House said US Vice President Joe Biden called Barzani on Saturday to express his condolences at the beheadings.
It said both men "agreed that such unconscionable acts of brutality reflect ISIL's true nature and reinforce our collective resolve to defeat ISIL", an alternative name for IS.
In February, IS released footage purporting to show more than a dozen peshmerga captives paraded in cages.
IS spearheaded a sweeping offensive that overran large areas north and west of Baghdad last year, and peshmerga forces moved into a swathe of disputed northern territory after federal security forces withdrew.
The jihadists have carried out numerous atrocities in areas they control, ranging from public beheadings to enslavement and rape.