The Islamic State is believed to have fired a shell containing mustard gas toward the Qayyara Military Base in Iraq Tuesday, where U.S. and Iraqi forces are operating, according to a report.
Several U.S. officials told CNN the device was either a rocket or an artillery shell. It was tested by U.S. troops shortly after landing on the base, which is just south of Mosul. Early indications revealed the shell contained a chemical agent thought to be mustard.
One official described the gas as "poorly weaponized" and "low purity," while a second said the shell was "ineffective." To date, no troops were hurt and none have displayed symptoms of exposure to mustard agent. Two of four soldiers who were near the device underwent complete decontamination treatment, Fox News reported.
"Unless you are right next to [the shell]," a U.S. official told reporters, "exposure is unlikely."
The remains of the shell will be sent to Ft. Detrick, Md., for processing to confirm whether it did, in fact, contain mustard agent, which leaves an oily residue.
Mosul is the last major Iraqi city controlled by the Islamic State.
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