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. The attack was first reported by CNN.

A Pentagon official told reporters that a “tar-like black oily substance” was found on the shell, which landed within the base hundreds of yards from U.S. forces. An initial test for the agent was positive, but “could be false,” the official said. The second test was negative, possibly because the shell had been exposed to the elements. No one was injured in the attack and there were “no signs of exposure” shown by any U.S. troops, including the two soldiers who inspected the shell. Two to four soldiers who were near the shell received full decontamination treatment. READ MORE