The identity of James Foley's killer may be soon revealed. British Ambassador to the United States Sir Peter Westmacott said on "Meet the Press" intelligence officials are "close" to identifying the executioner seen in the Islamic State's beheading video released Tuesday.

"I think we are close," said Westmacott. The ambassador said intelligence officials are using voice identification technology to identify Foley's executioner. Westmacott estimates 500 people from Britain have joined the group formerly known as the Islamic State in Iraq and Syria, or ISIS.

report in the Sunday Times, quoting "senior [U.K.] government sources, said Britain's domestic and foreign intelligence services, MI5 and MI6, respectively, have already identified the man seen in the Foley video. A Guardian report Wednesday said the executioner goes by John and is the head of a group in charge of foreign hostages.

Speaking on "Fox News Sunday," Sen. John McCain (R-Ariz.) said ISIS was the "greatest threat we've seen since 9/11. This has been festering for the last year and now it’s culminating with the killing and beheading of an American journalist, which I think is a turning point."

Following what the White House called ISIS' "first terrorist attack against the United States," other politicians are concerned the group may set its sights on western targets.

"They are intent on hitting the west. And there are external operations, I believe, on the way," Rep. Mike McCaul (R-Texas), chairman of the House Committee on Homeland Security, on ABC's "This Week."