Extremist Sunni militants the Islamic State posted a video apparently showing the murder of a captured Kurdish peshmerga fighter, and warned Iraqi Kurdish leaders to stop their close military cooperation with the US.

The footage, which was released Thursday, is titled "A message written in blood to the leaders of the American Kurdish alliance." It opens with 15 men in orange jumpsuits standing around a black Islamic State flag. Three of the fighters speak to the camera saying that their captors will kill the entire group of fighters if US-Kurdish cooperation continues. "Any mistake or recklessness from you will lead to the (loss) of our life," one of the men reportedly says.

Later, the video shows a man kneeling between three masked and armed black-clad militants in front of Mosul's Great Mosque, where propaganda film released in early July was said to show Islamic State leader Abu Bakr al-Baghdadi delivering a sermon.

One of the militants then appears to slit the man's throat as the picture fades to black. The footage then cuts to a scene of his decapitated head on top of his body. The video closes with a parade of Islamic State vehicles, including a number of armored personnel carriers seemingly looted from the Iraqi army.

The US launched a series of airstrikes on Islamic State targets in northern Iraq earlier this month, helping Kurdish forces retake ground lost to the group in a shock offensive. It has also supplied weapons and ammunition to the Kurdish Regional Government.

This video is similar to one released by the Islamic State on August 19 in which the group appeared to behead American journalist James Foley and threatened to kill Steven Sotloff, another kidnapped reporter, if the US did not stop the strikes.

President Barack Obama called for a coalition of countries to take military action against the Islamic State in Iraq and Syria on Thursday, and said the US was attempting to recruit partners potentially willing to do so. "We are going to work politically and diplomatically with folks in the region," Obama said. "And we're going to cobble together the kind of coalition that we need for a long-term strategy as soon as we are able to fit together the military, political and economic components of that strategy."

Foley and at least three other hostages held by the Islamic State in Syria, were tortured using the "waterboarding' technique, which simulates drowning, according to a report in the Washington Post on Thursday. The Post quoted sources familiar with Foley's time in captivity as saying he had been waterboarded on several occasions by people who "knew exactly how it was done." Another source added that they believed he had "suffered a lot of physical abuse."

The CIA used waterboarding as an interrogation technique during former president George W Bush's "war on terror", but was stopped after Barack Obama's election and designated a "cruel and unusual punishment."

On Thursday, the Islamic State also released footage said to show the remains of 250 Syrian soldiers that they had taken prisoner at Tabqa airbase, and subsequently executed. The base was the only point in the Islamic State-dominated Raqqa province still under control of Syrian government forces, but it fell to the militant group this week.

Another video was released simultaneously that claimed to show the prisoners being marched through the desert before they were killed.