Britain is close to identifying a man, thought to be British, who was shown beheading US journalist James Foley in a video released by the Islamic State militant group last week, its ambassador to the United States, Peter Westmacott, told CNN.
"We are close" to identifying the man in the video, Westmacott told CNN's "State of the Union" program on Sunday.
"We're putting a lot into it," he said, including using voice-recognition technology to track down the killer.
British authorities are trying to identify the man, who has a London accent and has been dubbed "Jihadi John" by British media. The masked figure beheaded Foley in a video released on Tuesday that also threatened a second captive American journalist, Steven Sotloff.
Foley was abducted in Syria in November 2012; Sotloff was kidnapped there in 2013.
Westmacott said the problem "goes beyond one horrendous criminal."
"People think maybe as many as 500 British subjects have gone to Syria and Iraq for this cause of jihad," he said.
Hundreds of young people from across Europe have left their homelands for Iraq and Syria, the Monitor's Sarah Miller Llana reported.
Driven by everything from anger at the mass killing of Muslims by the Syrian regime of Bashar al-Assad to a sense of idealism about joining a possible new religious state, young people are leaving the security of their families, their educations, and often their suburban lifestyles to support jihadi groups. Some of them are joining rebel movements linked to Al Qaeda. Others are aligning with even more-radical Islamic cells.
The young people are departing in large enough numbers to stir concern in top policy circles across Europe. According to figures from the International Center for the Study of Radicalization at King’s College London, as many as 2,000 Europeans have already fled to Syria. The French government estimates 700 young people have left from France alone – the largest number from any country on the Continent.
Up to 500 youths from Britain have joined Syrian rebel groups, more than 300 from Germany, and at least 100 from the Netherlands. Many Belgian teens have fled, too, as well as dozens from the United States. An American from Florida was linked to a suicide bombing in Syria in May.