The masked Islamic State militant known as "Jihadi John", who has been pictured in the videos of the beheadings of Western hostages, has been named, BBC reports.
He is Mohammed Emwazi, a Kuwaiti-born British man in his mid-20s from west London, who was previously known to British security services.
Emwazi was believed to have travelled to Syria around 2013 and later joined IS, which has declared the creation of a "caliphate" in the large swathes of Syria and neighbouring Iraq it controls.
Emwazi first appeared in a video last August, when he apparently killed the US journalist James Foley. He was later thought to have been pictured in the videos of the beheadings of US journalist Steven Sotloff, British aid worker David Haines, British taxi driver Alan Henning, and American aid worker Abdul-Rahman Kassig, also known as Peter.
In each of the videos, the militant appeared dressed in a black robe with a black balaclava covering all but his eyes and top of his nose.
Speaking with a British accent, he taunted Western powers before holding his knife to the hostages' necks, appearing to start cutting before the film stopped. The victims' decapitated bodies were then shown.
Hostages released by IS said he was one of three British jihadists guarding Westerners abducted by the group in Syria. They were known collectively as "the Beatles".
A spokeswoman for British Prime Minister David Cameron would not confirm or deny the latest reports, adding that the police and security services were working hard to find those responsible for the murder of the British hostages.