The UK is close to identifying a suspected jihadist who is believed to have beheaded a journalist, ambassador to the US Peter Westmacott has said.
The UK has been trying to identify the Islamic State militant with an English accent who appears in footage of the killing of US journalist James Foley.
"We are very close to identifying who this guy is," Westmacott told CNN.
Foreign Secretary Philip Hammond said the death was a "betrayal of everything the British people stand for".
Westmacott also told NBC's Meet the Press: "We're not in a position to say exactly who this is but I think we are close."
Referring to the 500-plus British citizens who are thought to have travelled to Syria and Iraq to fight in the past few years, he said: "It's not just about one brutal murderer - it is a threat to our citizens."
The AFP news agency, meanwhile, quotes Westmacott as saying: "I can't say more than this but I know from my colleagues at home that we are close.
"We're putting a lot into it and there are sophisticated technologies, voice identification and so on which people can use to check who these people are," Westmacott said.
Westmacott 's comments come after Foreign Secretary Hammond wrote in the Sunday Times that the government was investing "significant resources" to tackle "a barbaric ideology".
He said the threat from conflicts in Syria and Iraq could last a generation.