DETECTIVES have launched an investigation after a video showing the execution of the American journalist James Foley was posted on a Bolton Facebook page.

Police said the shocking video was posted on the Stop the Astley Bridge Mosque page soon after it emerged online last month.

The disturbing film of Mr Foley’s brutal killing, which was released by terror group Islamic State (IS) on August 19, showed the 40-year-old, kneeling in a desert-like environment as an IS fighter stood by his side dressed in black, with his face covered.

The Metropolitan Police warned that “viewing, downloading or disseminating extremist material” in the UK may constitute an offence under terrorism legislation.

Ch Insp Mark Bell said: “Police in Bolton are aware that the video showing the execution of an American journalist has been posted on a local Facebook site.

“As the Metropolitan Police have outlined, to download, share or post this video could be a criminal offence so we will be investigating this matter to ascertain who has posted it and what offences may have been committed.”

The Stop the Astley Bridge Mosque Facebook page was set up to oppose plans to extend a mosque in Blackburn Road and police said they were monitoring the page.

It is understood the video was posted on the page on August 22 but deleted at a later date.

An administrator for the page said he had been away for a few days and was not aware the video had been posted.

Supt Andrea Jones said: "Greater Manchester Police continually monitors social networking sites such as the Stop The Astley Bridge Mosque page to ensure that free speech does not turn into racist comments or religiously motivated comments that could be considered criminal.

“If anyone does find these comments offensive or racist, we would encourage people to report them to us so we can investigate.

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"Anyone who is found to have posted offensive or criminal remarks on social networking sites faces prosecution.”

A spokesman for Facebook said the video was reported to them and then removed for breaking the site’s community standards.

YouTube and Twitter said they were taking action to remove any video of the murder.

Mr Foley, who worked for organisations including Agence France-Presse, went missing in Syria in 2012.

Following the killing, thousands of people, including celebrities and scores of fellow journalists, took to social media to urge people not to give IS the oxygen of publicity.

Prime minister David Cameron has announced new laws to crack down on terror suspects as he warned that extremism in Iraq and Syria poses a greater danger to Britain than al Qaida.

As the terrorist threat to the UK was raised from substantial to severe, the prime minister said legislation would be introduced so it was easier to seize jihadists’ passports.

He said: “What we are facing in Iraq now with Islamic State is a greater threat to our security than we have seen before.”

A second video, showing the apparent murder of another American journalist, Steven Sotloff, was released by IS militants on Tuesday.