President Obama Confirms That Peter Kassig Has Been Killed By Isis (Watch Video)

The Islamic State of Iraq and Syria (ISIS) group has beheaded Peter Kassig, releasing a video Sunday showing a masked militant standing over the severed head of a man it said was the former U.S. Army Ranger-turned-aid worker, who was seized while delivering relief supplies in Syria last year.

U.S. President Barack Obama confirmed Kassig's slaying after a U.S. review of the video, which also showed the mass beheadings of a dozen Syrian soldiers.

The 26-year-old Kassig, who founded an aid group to help Syrians caught in their country's brutal civil war, "Was taken from us in an act of pure evil by a terrorist group that the world rightly associates with inhumanity," Obama said in a statement.

He denounced the extremist group, which he said "revels in the slaughter of innocents, including Muslims, and is bent only on sowing death and destruction."