An ISIS leader tied to the killing of an American aid worker in 2014 was killed in an airstrike, a military representative said Monday.

The U.S.-led coalition fighting ISIS conducted drone strikes on Sunday against Abu al-Umarayn and several other IS members, Col. Sean Ryan, a spokesman for said coalition fighting, told the Associated Press. He also said that al-Umarayn was believed to be “posing an imminent threat” to coalition workers.

The strikes took place in a desert area in southeastern Syria.

Abu al-Umarayn was “involved in the killing” of military veteran Peter Kassig, 26, who was beheaded Nov. 16, 2014, according to Col. Ryan.

Kassig was captured thirteen months prior and held with other journalists until his death.

On the day of Kassig’s death, ISIS posted a 16-minute video online showing them beheading around a dozen Syrian soldiers and the video concluded with a militant standing over a severed head that he claims is Kassig, according to a story from Reuters.

Former President Barack Obama called the murder at the time “an act of pure evil by a terrorist group that the world rightly associates with inhumanity.”

Kassig was an Indiana native and served in Iraq in 2007 in the U.S. Army’s 75th Ranger Regiment. (RELATED: ISIS Beheads American Journalist Steven Sotloff)

In 2012, Kassig founded a humanitarian non-governmental organization aimed at helping Syrians affected by the ongoing civil war. He reportedly fell into the hands of ISIS after being captured in October of 2014. While in captivity, Kassig converted to Islam and changed his name to Abdul-Rahman Kassig. (RELATED: ISIS Beheads British Aid Worker David Haines)

Follow Mike on Twitter