First on CNN: ISIS suspected of mustard attack against US and Iraqi troops
Updated 5:29 PM ET, Wed September 21, 2016
The shell was categorized by officials as either a rocket or artillery shell. After it landed on the base, just south of Mosul, US troops tested it and received an initial reading for a chemical agent they believe is mustard.
No US troops were hurt or have displayed symptoms of exposure to mustard agent.
(CNN)