US President Barak Obama praised Peter kassig as a humanitarian killed in "an act of pure evil" by the Islamic State
Kassig, a 26-year-old from Indiana, is also known as Abdul-Rahman, a name he took following his conversion to Islam while in captivity.
Kassig's parents have said through a spokesperson their son was taken captive on his way to the eastern Syrian city of Deir al-Zor on Oct. 1, 2013.
A former soldier, Kassig was doing humanitarian work through Special Emergency Response and Assistance, an organization he founded in 2012 to help refugees from Syria, the family has said.
If confirmed, Kassig's beheading would be the fifth such killing of a Westerner by Islamic State, following the deaths of two US journalists and two British aid workers.