By Scott Shane

New York Times News Service

The British ambassador to the United States said Sunday that investigators were close to identifying the young militant with a British accent who beheaded American journalist James Foley on a video released last week by the Islamic State.

The ambassador, Peter Westmacott, said in an interview on CNN that British counterterrorism officers, supported by their American counterparts, were making progress in using clues in the video to pick the killer out of the hundreds of British Muslims who had joined the Islamic State group.

“I do know from my colleagues at home that we are close,” he said. “But forgive me if I can’t go much further than that at this point.”

Westmacott said investigators were trying to match the killer’s voice against recordings of known British militants now in Syria and Iraq. “We’re putting out a great deal of resource into identifying this person,” he said. “And there are some very sophisticated technologies, voice identification and so on, which people can use to check who these people are.”

If Foley’s killer is identified, it might give intelligence officials insight into the Islamic State kidnapping cell still holding another American reporter, Steven Sotloff, and other hostages, and could lead to criminal charges.

But with extremists in control of large parts of Syria and Iraq, it would be hard even to locate the suspect and highly risky to try to take him into custody anytime soon. An attempt early this summer by American Delta Force commandoes to rescue Foley and others held in Syria failed because the hostages had been moved.

“If things stay the way they are now, it would be difficult” to kill or capture the suspect, said a senior U.S. law enforcement official, who spoke on the condition of anonymity because of the continuing investigation. The official said that the FBI and CIA, working with their British counterparts, MI-5 and MI-6, had narrowed to “a short list” the suspects in Foley’s killing.

The five-minute video released by Islamic State, now the focus of intensive forensic analysis by British and American authorities, is narrated in part by the apparent killer, wearing a black hood with eyeholes, who addresses the camera in English before putting a knife in his left hand to Foley’s throat. He then begins a sawing motion before the video skips ahead to show Foley’s severed head atop his corpse in the sand, with what appears to be a different knife lying nearby.

From an analysis of the video images, investigators could estimate the man’s height, study details of his eyes and eyebrows, and note his evident left-handedness. His voice likely has been matched against recordings of many of the estimated 500 militant Britons who have joined the Islamic State group, about half of whom are believed to have returned home.

British counterterrorism agencies conduct extensive eavesdropping in the United Kingdom on people suspected of being extremists and have archived recordings of many of them. In addition, some foreigners who have joined Islamic State have left long Web trails that include audio of their voices on YouTube and other sites.

The Foley video, which incorporated footage of President Barack Obama’s announcing American airstrikes on Islamic State and Foley’s final words to his family, reflects the sophistication of Islamic State’s extensive media efforts, aimed in part at recruiting more fighters from the West, said Rita Katz, director of the SITE Intelligence Group, which monitors extremist communications.

While Obama said last week that “the entire world is appalled by the brutal murder” of Foley, the president’s remarks did not take into account many young Muslims who support Islamic State and have been vocal in their praise of Foley’s death and the video in particular, Katz said. Some Twitter users posted excited praise for the video, and a few took images from the beheading video to use as their profile pictures on social media sites.

“Did you see what we can do? There is more!!” wrote one Islamic State supporter monitored by SITE. Another wrote, “I was happy to see the beheading of that kaafir.” Kaafir is the Arabic word for unbeliever.

To judge by Twitter and other social media, “British militants have been impressed that this was done by a British guy,” said Raffaello Pantucci, director of international security studies at the Royal United Services Institute and author of a coming book about Muslim extremists in Britain.

Far from sharing the revulsion of most viewers, those who see Islamic State as defending Islam from Western aggression found the video “empowering,” Pantucci said. “They say, ‘Look at what we can do, and the powerful Americans can’t do a thing about it.’ They feel they’re part of a community that accepts this and thinks it’s a glorious thing to do.”

Other hostages held by Islamic State have said they began calling their British captors by the names of the Beatles, and the killer of Foley was known as “John,” with others nicknamed “Paul” and “Ringo.” British and American authorities have so far been unwilling to say who they believe the killer to be, perhaps because to name him without being able to capture or kill him would simply add to his luster in the extremist world.