ISIS fighters are believed to have attacked U.S. and Iraqi forces with a "crude" chemical weapon Tuesday evening, a U.S. official told Fox News. The U.S base outside Qayyarah, 25 miles south of Mosul, was struck by a rocket and traces of a "mustard agent" were believed to be present, the official said. Nearly 5,000 U.S. troops are currently on the ground in Iraq and "hundreds" of those forces are located at the base, the official said. for processing to confirm the presence of a chemical agent. Unlike mustard gas, which can spread, mustard agent leaves an oily residue behind.

Source: Fox News September 21, 2016 21:26 UTC