A video circulated Sunday purporting to show an Islamic State execution of five men it said were spying for Britain in Syria.
The 10-minute clip depicted the men allegedly confessing to espionage, filming and photographing, in exchange for money, the location of militants in Raqqa, the northern Syrian capital of the Islamic State's self-declared caliphate. The men wore orange jumpsuits, kneeling before five masked fighters in military fatigues who brandished pistols.
One of the gunmen said the execution was "a message to David Cameron," the British prime minister, who has ramped up attacks on Islamic State insurgents in Iraq and Syria.
"How strange it is that we find ourselves today hearing an insignificant leader like you challenge the might of the Islamic State," the gunman said. He vowed that the Islamic State would "one day invade your land, where we will rule by the sharia," referring to a strict code of Islamic law.
The purported spies were then shot in the head.
The British foreign office said it was aware of the video and was examining it.