ISIS likely used mustard gas in an attack on Kurdish forces in Iraq this week, according to senior U.S. officials. In addition, there was another reported incident of chemical weapons use in Syria in “recent weeks,” according to an NBC News report. A defense official told The Daily Beast that the Pentagon believes these reports “to be credible.” The self-proclaimed Islamic State has had a longstanding interest in unconventional arms. Earlier this year, an American airstrike near Mosul, Iraq, killed an ISIS chemical-weapons specialist.
Other forces in the Syrian civil war have also pursued—and used—such weapons. The Bashar al-Assad regime in Syria contended that all of their chemical weapons were destroyed after a 2013 agreement with the major world powers. But inspectors were never able to fully verify those claims, and Western inteligence services have long believed that Assad has a second, secret chemical stockpile.