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.

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.

US judge orders release of Iraq prisoner abuse photos
New York (AFP) March 21, 2015 - A United States judge has ordered the government to release a trove of photos depicting abuse of detainees in Iraq and Afghanistan in the latest twist to a long-running legal battle over the images.

In a ruling issued in New York on Friday, US federal judge Alvin Hellerstein gave the government two months to decide how to respond to his order before the photos could be released.

The case has been brought by the American Civil Liberties Union which argues the release of the photos is necessary for an "ongoing national debate about governmental accountability for the abuse of prisoners."

The US government has opposed the release of the photos on the grounds they could provoke a violent backlash and place US forces and personnel overseas at heightened risk of attack.

Congress passed a law in 2009 known as the Protected National Security Documents Act, which allows for the US secretary of defense to withhold the release of documents that are deemed to endanger US personnel.

However in Friday's ruling, Hellerstein said the US government had provided insufficient justification for attempting to block the release of the photos under the 2009 legislation.

"I found that the certification remained deficient because it was not sufficiently individualized and it did not establish the (defense) secretary's own basis for concluding that disclosure would endanger Americans," Hellerstein wrote.

The order could see the release of around 2,000 photos according to the ACLU. The exact content of the images is not known, but a government brief filed earlier in the court case said several photos showed "soldiers pointing pistols or rifles at the heads of hooded or handcuffed detainees."

The ACLU's deputy legal director Jameel Jaffer welcomed Friday's ruling.

"The photos are crucial to the public record," Jaffer said.

"The Obama administration's rationale for suppressing the photos is both illegitimate and dangerous.

"To allow the government to suppress any image that might provoke someone, somewhere, to violence would be to give the government sweeping power to suppress evidence of its own agents' misconduct."

US soldiers were implicated in the torture and sexual humiliation of Iraqi prisoners at Baghdad's Abu Ghraib prison when the US military ran it in 2004, a scandal that first broke when photos showing soldiers abusing detainees were published in US media.

Between 2004 and 2006, 11 soldiers -- including Lynndie England, who was seen smiling beside naked prisoners being subjected to sexual abuse -- were convicted in court martials.

Pentagon spokesman Lieutenant Colonel Myles Caggins said the Defense Department was "studying the judge's ruling and will make any additional responses through court filings."