(CNN) The U.S. government has test results from an ISIS attack in Hasakah, Syria, from two weeks ago that confirm the terror group used a mustard agent as a weapon, multiple U.S. intelligence and military officials told CNN on Friday.
The U.S. is continuing to investigate an attack this week in northern Iraq that also has indications of a similar chemical agent being used.
Officials stress the amount of chemical agent is thought to be small and the concentration low. But it is yet another sign that ISIS is in possession of mustard agent and is using it in battle.
Advertisement - story continues below