The SITE Intelligence Group said the video shows five men from Raqa, capital of the self-declared jihadist 'caliphate' straddling Syria and Iraq, confessing to carrying out acts of espionage.
In it, an English-speaking IS fighter mocks British Prime Minister David Cameron for challenging IS, and calls him an 'imbecile'.
The 'confessions' of the five do not clearly identify which countries they worked with, but one mentions the international coalition led by the United States battling against IS in Iraq and Syria.
The video said they passed videos or photos of the living conditions in Raqa to people in Turkey, or monitored the movements of IS fighters. The following sequence shows the five wearing orange jumpsuits and kneeling before five masked fighters, all in military fatigues and armed with pistols. "This is a message to David Cameron," says one of the gunmen.
"How strange it is that we find ourselves yesterday hearing an insignificant leader like you challenge the might of the Islamic State."  British warplanes, which were already attacking IS positions in Iraq, at the beginning of December began targeting the jihadists in Syria also.
"Only an imbecile would dare to wage war against a land where the law of Allah reigns supreme and where the people live under the justice and security of sharia" or Islamic law, the fighter says.

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