Report: ISIS May Have Used Chemical Weapons on U.S. Forces

No U.S. troops showed symptoms of exposure to nerve agent, CNN says citing officials.

ARCHIVE - In this Wednesday, Aug. 28, 2013, investigators take samples near a part of a missile that was suspected of carrying chemical agents in Ain Terma, Syria.AP

REUTERS - Islamic State forces fired a shell that may have contained a chemical agent onto a military base in northern Iraq on Tuesday while U.S. and Iraqi troops were present, CNN reported on Wednesday, citing several U.S. officials. 

No U.S. troops were hurt in shelling at the base, which is being used to prepare an attack to retake Mosul from Islamic State, CNN said. 

The first test came back positive for a mustard agent but the second test was negative, it said.