World appalled by American journalist's beheading: Obama

The entire world is appalled by the brutal murder of American journalist James Foley, US President Barack Obama said Wednesday.

Obama said he had spoken to the Foley family and told them that "we are all heartbroken at their loss, and join them in honouring Jim and all that he did", Xinhua reported. The statement came shortly after the authenticity of a video showing the American journalist's beheading had been verified.

Foley, a freelance American journalist who was captured by militants in Syria in November 2012, was shown on a video being beheaded by a masked militant from the Islamic State to avenge ongoing air raids on the group's targets by US warplanes.

Obama praised Foley for being "a man who lived his work, who courageously told the stories of his fellow human beings and who was liked and loved by friends and family".

"Today, the American people will all say a prayer for those who loved Jim. All of us feel the ache of his absence. All of us mourn his loss," Obama said from Martha's Vineyard, Massachusetts during his vacation.

His statement came shortly after the White House said that the video showing the beheading of Foley had been authenticated by the US intelligence community.

IS militants, which have seized large swathes of territories in western and northern Iraq in recent months, also threatened to kill another man shown on the video said to be American freelancer Steven Sotloff.

The US will continue to "do what we must do to protect our people," Obama said, vowing that "when people harm Americans, anywhere, we do what's necessary to see that justice is done".

"ISIL has no ideology of any value to human beings. Their ideology is bankrupt," the president added.