British Prime Minister David Cameron has cut his holiday short following the release of a propaganda video from Islamic State (IS), purportedly showing the beheading of US journalist James Foley, apparently by a Briton.

Cameron returned to London for meetings with ministers about how to deal with the increasing threat posed by IS in Syria and Iraq.

In the clip the jihadist who carried out the killing speaks with a British accent and blames US airstrikes in Iraq for Foley’s murder.

The clip, which is still being verified, has sent chills around the globe.

In it, Foley was forced to read a statement blaming America and even his own brother John – who is in the US Air Force – for his killing.

The terrorist then warns that another journalist, Steven Joel Sotloff, will be their next victim.

Foley was taken hostage in November 2012 while covering the Syrian war for news website GlobalPost. He had previously been kidnapped and released in Libya.

Foley’s mother said her son gave his life to expose the suffering of the Syrian people.

On Twitter, hundreds of users urged the public to neither watch nor share the video, which was taken down shortly after it was uploaded.

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