Abdul-Rahman (Peter) Kassig is pictured collecting bread for a delivery to refugee populations in this undated handout photo.

DAMASCUS — “Islamic State” militants have beheaded another American hostage, Peter Kassig, issuing a video claiming the killing on Sunday and warning the United States they would kill other U.S. citizens “on your streets.”

President Obama confirmed the death of the aid worker in what he called “an act of pure evil by a terrorist group that the world rightly associates with inhumanity.”

The announcement of Kassig’s death, the fifth such killing of a Western captive by the group, formed part of a 15-minute video posted online in which “Islamic State” showed the beheadings of at least 14 men it said were pilots and officers loyal to Syrian President Bashar al-Assad.

Kassig, 26, from Indiana, was also known as Abdul-Rahman, a name he took after converting to Islam in captivity. His family has said he was taken captive on his way to the Syrian city of Deir al-Zor on Oct. 1, 2013.

“We are heartbroken to learn that our son, Abdul-Rahman Peter Kassig, has lost his life as a result of his love for the Syrian people and his desire to ease their suffering,” Ed and Paula Kassig said in a statement. “Our heart also goes out to the families of the Syrians who lost their lives, along with our son.”

The video did not show the beheading of Kassig, who previously served in the U.S. Army, but showed a masked man standing with a decapitated head covered in blood at his feet. Speaking in English in a British accent, the man said: “This is Peter Edward Kassig, a U.S. citizen.”

French authorities identified two of the executioners who appeared in the video as French citizens. Michaël Dos Santos and Maxime Hauchard were described as recent converts to Islam.