LONDON - The British militant who beheaded US journalist James Foley is an "intelligent, educated and a devout believer in radical Islamic teachings", according to a British newspaper.
Sources told The Guardian that the militant, who called himself "John", is the leader of a group of British jihadists holding foreign hostages in Syria.
As an international manhunt got under way on Wednesday, the English-speaking militant with a British accent was identified to The Guardian by one of his former hostages as the ringleader of three British jihadists thought to be the main guards of foreign nationals in Raqqa, a stronghold of Islamic State (Isis) rebels.
The militant who appeared on the Foley video is believed to be from London, the paper said. He was also believed to be the main rebel negotiator during talks earlier this year to release 11 Islamic State hostages - who were eventually handed to Turkish officials after ransom demands were met.
The FBI, MI5 and Scotland Yard's counter-terrorism command were all on Wednesday night racing to identify the militant who fronted the propaganda video that showed the brutal murder of Foley, the American journalist who had been missing in Syria since 2012.
British Prime Minister David Cameron said on Wednesday it seemed "increasingly likely" that a British jihadist executed Foley, AFP reported.
"We have not identified the individual responsible, but from what we have seen it looks increasingly likely that it is a British citizen.
"This is deeply shocking. But we know that far too many British citizens have travelled to Iraq and travelled to Syria to take part in extremism and violence. And what we must do is redouble all all our efforts to stop people from going."
Sources in Syria recognised "John" as a point-man for hostage negotiations in Raqqa, where he is said to have held discussions with several families of jailed foreign nationals over the internet, the Guardian said.
One former hostage, who was held for a year in Raqqa, told the Guardian the British executioner is intelligent, educated and a devout believer in radical Islamic teachings. The three UK-born militants were referred to as "the Beatles" by fellow hostages because of their nationality, the former captive added.
Experts in the the counter-terrorism and linguistics fields said the man appeared to be one of up to 500 British-born jihadists "brutalised" by Isis after fleeing Britain to fight in Syria and Iraq.
Security services in Britain and US were analysing the propaganda footage, with forensic phonetics experts among those thought to be involved in trying to identify the masked militant from his accent.
Prof Paul Kerswill, a linguistics expert at the University of York, said he believed the man spoke in "multicultural London English" most commonly found in London's East End, the Guardian reported.
"He probably has a foreign language background but it sounds like multicultural London English, which is people from all kinds of backgrounds who mix in the East End, a new kind of cockney," he said.
Dr Claire Hardaker, a linguistics experts at Lancaster University, studied the clip and said the man's vowels marked him out as likely from the south-east of England, but most likely from London. "We're definitely looking at a British accent, from the south, and probably from London, Kent or Essex."
Prof Peter Neumann, director of the International Centre for the Study of Radicalisation, at King's College London, said an English-speaking militant was chosen deliberately to front the video to cause maximum impact in the west.
"This is significant because it signifies a turn towards threatening the west. They are saying we're going to come after you if you bomb us."