The Islamic State group claimed to have beheaded three Iraqi Kurdish fighters in an online video and threatened to kill more unless the Kurds stop bombardment of jihadist-controlled areas.

Peshmerga forces from Iraq's autonomous Kurdish region, backed by US-led air strikes, are battling IS in the country's north and have pushed the jihadists back in Nineveh and Kirkuk provinces.

The video starts with images of people being brought to a hospital and a voiceover saying that they were wounded by peshmerga rocket fire.

The three prisoners, dressed in orange jumpsuits with their hands bound, are later shown kneeling one at a time with masked militants standing guard at locations said to have been hit by peshmerga fire, and are then beheaded.

People including young children are visible looking on in the background.

The video was said to have been filmed in Nineveh province, though the exact location was unclear, and there was no immediate confirmation from Kurdish authorities that the victims were peshmerga.

One militant addressed Kurdish regional president Massud Barzani, saying that with "every rocket you launch against the Muslims... you will kill one of your prisoners with your hands."

In February IS released a video purporting to show more than a dozen peshmerga hostages 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.