BEIRUT (AP) — Islamic State group militants are claiming another beheading, this time of captured U.S. aid worker Peter Kassig.

In a graphic, nearly 16-minute video uploaded to social networks today, a black-clad militant with his face concealed stands before a severed head. The video also shows what appears to be the mass beheading of several captured Syrian soldiers. It was not immediately possible to confirm that Kassig is pictured in the video.

The video, posted on websites used by the group in the past, appears to be the latest in a series of grisly messages to the U.S. warning of further brutality if it does not abandon its air campaign in Iraq and Syria.

Kassig, a U.S. Army Ranger, was providing medical aid to Syrians fleeing the country's civil war when he was captured inside Syria on Oct. 1, 2013. His friends say he converted to Islam in captivity and took the first name Abdul-Rahman.

Kassig's family has says they are aware of reports regarding the death of their “treasured son” but are awaiting government authentication. His parents requested in a statement Sunday, that their family's privacy be respected.

The latest video did not show the person identified as Kassig being beheaded.