The FBI is asking the public's help in identifying an English-speaking man who appears in a propaganda video released last month by the Islamic State extremist group.
Most of the man's face is covered, but the agency said Tuesday that his accent is believed to be North American and that it hopes viewers can help identify his voice and appearance.
The FBI posted a segment of the video online. It shows the man standing in front of people he says are digging their own graves in the eastern Syrian province of Raqqah. Later in the nearly hourlong video, released Sept. 19, he presides over their executions.
When it comes to helping identify the man, "no piece of information is too small," Michael Steinbach of the FBI Counterterrorism Division said in a statement.
The FBI is also asking the public to tell it about Americans who have traveled overseas to fight alongside Islamist militant groups or who are planning to do so.
Islamic State fighters have seized broad swaths of Syria and Iraq and in June proclaimed a caliphate in that territory, where they have targeted fellow Muslims and adherents of other faiths. The Al Qaeda splinter group has killed thousands of people, and its tactics against Muslims it considered heretics are so savage that Al Qaeda's leaders disowned the group this year.
Starting in August, a U.S.-led campaign has been aiming airstrikes at the group's strongholds.
FBI Director James B. Comey said recently that about a dozen Americans were believed to be fighting in Syria alongside the Islamic State and that more than 100 Americans had been arrested on suspicion of trying to go to Syria or have gone there and returned.
On Saturday, a 19-year-old man from the Chicago area was arrested at O'Hare International Airport on suspicion of trying to travel overseas and join the extremist group.