The Islamic State group released a graphic video on Sunday in which a black-clad militant claimed to have beheaded U.S. aid worker Peter Kassig, who was captured last year.
The militant was standing over a severed head, but it was not immediately possible to confirm that it was Kassig, 26, who was pictured in the video. U.S. officials said they were working to determine the video's authenticity and the Kassig family said it was awaiting the outcome of the investigation.