White House says beheading video authentic

The Barack Obama administration Wednesday confirmed the authenticity of a video showing the decapitation of a US journalist who was abducted in November 2012 while covering the civil war in Syria.

"The US intelligence after analysing the recently released video showing James Foley and Steven Sotloff have reached the judgment that this video is authentic," National Security Council spokeswoman Caitlin Hayden said in a statement.

The clip, produced by the Islamic State (IS) group, featuring the execution of Foley, 40, who was reporting for the US-based online news portal GlobalPost at the time of his abduction, proclaimed a caliphate in parts of Syria and neighbouring Iraq.

"The FBI Wednesday morning told the Foley family that they believe the video is authentic," the White House statement said.

Titled "A Message To America", the video includes footage of President Obama's announcement authorising the US airstrikes against IS in northern Iraq.

Speaking in English, the black-clad executioner warns that Obama's authorisation of air strikes against the IS hideouts.

"Any attempt by you, Obama, to deny Muslims liberty and safety under the Islamic caliphate, will result in the bloodshed of your people," the militant added before decapitating Foley. The US journalist's severed head appears on his lifeless body.

Next, an ISIS fighter appears standing next to Sotloff, a freelance journalist, who went missing in Syria about a year ago.

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