"We are aware of a video that claims to show the murder of US citizen Peter Kassig by IS. The intelligence community is working as quickly as possible to determine its authenticity," National Security Council Spokesperson Bernadette Meehan said.
"If confirmed, we are appalled by the brutal murder of an innocent American aid worker and we express our deepest condolences to his family and friends. We will provide more information when it is available," Meehan said.
Kassig, 26, was captured last year while helping provide medical aid to Syrians. His friends say he converted to Islam in captivity and changed his name to Abdul-Rahman.