US, UK Closing in on Identity of Foley Executioner, Sources Say

WASHINGTON — -- U.S. and British intelligence are closing in on the identity of the man who killed American journalist Jim Foley in a horrifying video that was released online, ABC News has learned.

"We are confident he will be identified," a senior U.S. official tells ABC News, adding he expected the positive identification to happen "soon."

Using voice recognition technology, intelligence agencies are working to match the voice on the video of Foley's execution with a voice database of British nationals with terrorist ties. They are also attempting to match the voice with communications now being monitored.

ABC News has also learned that U.S. officials know about three Americans in addition to Foley who were captured and held by ISIS -- Steven Sotloff and two aid workers.

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The White House said Wednesday that the video released earlier this week showing the murder of Foley at the hand of an Islamic militant "is authentic," a determination that came just before British Prime Minister David Cameron said it looked "increasingly likely" the masked executioner was from the United Kingdom.

The gruesome video, released online Tuesday, appeared to show an armed militant, who identified himself as with the Islamic State of Iraq and Syria, beheading Foley.

Before his death, Foley delivered a halting, potentially coerced statement condemning U.S. military efforts against ISIS, and the figure clad in black spoke directly to President Obama with what seemed to be a British accent.

After the figure in black kills Foley, he threatens another American hostage, Steven Sotloff, saying, "The life of this American citizen, Obama, depends on your next decision."

Prior to the video's release, the U.S. military launched dozens of airstrikes on ISIS targets in support of a Kurdish and Iraqi military offensive against the terror group at and around the Mosul Dam, eventually pushing the extremists off the key piece of infrastructure.