LONDON, England (AFP) — Prime Minister David Cameron said yesterday it seemed “increasingly likely” that US journalist James Foley was beheaded by a British jihadist, as experts sought to identify the English-accented executioner.

Cameron, who broke off his holidays for emergency meetings on the threat posed by Islamic State militants operating in Iraq and Syria who orchestrated Foley’s execution, said the killer’s probable nationality was “deeply shocking”.

Following talks with senior ministers at his Downing Street office in London, he said “far too many” Britons had travelled to the region to join jihadist groups and spelled out measures to combat extremism.

“Let me condemn the barbaric and brutal act that has taken place and let’s be clear what this act is — it is an act of murder, and murder without any justification,” Cameron told reporters.

“We have not identified the individual responsible, but from what we have seen it looks increasingly likely that it is a British citizen.”

Scotland Yard, which leads counter-terror policing in Britain, confirmed it was investigating footage of the killing.

“The Metropolitan Police Counter Terrorism Command is investigating the contents of the video that was posted online,” it said.

The footage showed a masked militant with an English accent beheading Foley, who has been missing since he was seized in Syria in November 2012.

Cameron also said London would work with the new Iraqi government, help arm the Kurdish forces fighting Islamic State militants in northern Iraq and use Britain’s aid, diplomacy and “military prowess” to put pressure on “this appalling organisation”.

The Guardian newspaper, citing an unnamed former hostage, claimed the executioner could be the leader of a group of “British fighters” that has guarded foreign hostages in Syria.

The paper reported that the man was called John and hailed from London.

The newspaper cited linguistics experts who said the executioner has a “British accent, from the south” and spoke “multicultural London English”.