The video appears to show US journalist James Foley being beheaded YouTube

Militant group Islamic State - formerly Isis - has posted a graphic video apparently showing the beheading of US journalist James Wright Foley, who went missing in Syria in 2012.

When your colleagues dropped that bomb on those people – they signed my death certificate
- James Foley

In the video, Foley is seen kneeling in the sand in an orange overall similar to those worn by detainees at Guantanamo Bay. Above him stands a figure clad in black holding a long knife.

In a clear, calm voice Foley says his death is the fault of the US for attacking Isis: "I call on my brother John, who is member of the US Air Force, think about what you are doing, think about lives you destroy including those of your own family. I call on you John, think about who made the decision to bomb Iraq recently and kill those people, whoever they may have been."

Foley had been abducted before, in Libya by pro-Gadaffi forces, but refused to stay away from danger, heading to Syria to document the horrors of war.

Yazidi ISIS US Islamic State
Displaced people from the minority Yazidi sect, fleeing Islamic State militants Reuters

In the video, in which he appears to be reading from cue-cards, Foley refers again to the US air strikes: "Think John, who did they really kill? Did they think about me, you our family when they made that decision? I died that day John, when your colleagues dropped that bomb on those people – they signed my death certificate."

The figure in black, speaking calmly and clearly in what sounds like an English accent, explicitly blames President Obama's decision to attack IS in Iraq: "You are no longer fighting an insurgency. You are fighting an Islamic army and a state that has been accepted by a large number of Muslims worldwide."

The video then appears to show the beheading of Foley by the man in black.

White House National Security Council spokeswoman Caitlin Hayden said the administration was attempting to determine of the video was genuine, and if it was, the US would be "appalled by the brutal murder of an innocent American journalist."

Ominously, the Islamic State video then shows the missing journalist Steven Joel Soltoff, also in orange, in a similar pose to that of Foley. The killer warns that if America's attacks continue, Soltoff will be next to die.

"The life of this American citizen, Obama, depends on your next decision."