Islamist militants 'kill reporter James Foley on video'

The Islamic State militant group has released a video online purporting to show the beheading of US journalist James Foley, missing since 2012, the BBC reported.

The militants said the killing was revenge for US air strikes against the Islamic State group in Iraq.

Foley's mother Diane said on Facebook she was proud of her son: "He gave his life trying to expose the world to the suffering of the Syrian people."

The White House said if the video was genuine, the US would be "appalled."

Foley has reported extensively across the Middle East, working for America's Global Post and other media outlets including the French news agency AFP.

In the video titled A Message to America, a man who appears to be James Foley is dressed in orange kneeling in desert-like terrain beside an armed man dressed in black.

The militant, who speaks with a British accent and identifies himself as an IS member, says the journalist's death is the direct result of US bombing of IS targets in Iraq.

In a statement, the Global Post asked for "prayers for Jim and his family", adding that it was waiting for the video to be verified.

In a 2012 interview with the BBC, Foley described his motivation for covering conflicts.

"I'm drawn to the drama of the conflict and trying to expose untold stories," he said.

"There's extreme violence, but there's a will to find who these people really are. And I think that's what's really inspiring about it."