The Islamic State (IS/ISIS/ISIL) released a video on Sunday showing what the group claims is the severed head of American aid worker Peter Kassig.

Kassig, who previously served the United States military as an Army Ranger, was captured last year while delivering medical aid to a region in northern Syria.

In the video, the jihadi executioner says to the camera, while standing above what he claims is the severed head of Kassig:

This is Peter Edwards Kassig, a US citizen of your country. Peter, who fought against the Muslims in Iraq whilst serving as a soldier in the American army, doesn’t have much to say. His previous cellmates have already spoken on his behalf.

“But we say to you Obama. You claim to have withdrawn from Iraq four years ago. We said to you then that you were liars, that you had not withdrawn. And that if you had withdrawn you would return even after some time – you would return.”

The masked jihadi continued:

Your forces will return greater in number than they were before. We also remind you of the haunting words of our Sheikh Abu Musab al-Zarqawi told you. The spark has been lit here in Iraq and it’s heat will continue to intensify by Allah’s permission until it burns the crusader army.

The ISIS militant then says his group intends to kill and bury American troops under Syrian soil, “eagerly waiting for the remainder of your armies to arrive,” he taunts.

Kassig had recently converted to Islam and had changed his name to Abdul-Rahman, according to reports. What remains unclear is Kassig’s motivation and intentions behind his conversion to the Muslim faith. Whether he was forced to do so, or converted in hopes to have the militants spare his life, remains largely unknown.

He was deployed to Iraq in 2007 while serving the military as an Army Ranger. He would later return to the region on a humanitarian mission to help refugees from the Syrian Civil War.

In October, Kassig’s parents pled with the Islamic State to release their son. Kassig’s father, Peter, requested of the ISIS militants, “We implore his captors to show mercy, and use their power to let our son go.” Kassig’s mother, who was wearing a Hijab, stated, “We implore those who are holding you to show mercy, and use their power to let you go.”

In a 2012 interview with CNN, Kassig said of his mission: “We each get one life and that’s it. The way I saw it, I didn’t have a choice. This is what I was put here to do. I guess I am just a hopeless romantic, and I am an idealist, and I believe in hopeless causes.”