Isis militants are suspected of firing a shell loaded with a chemical agent during an attack on US and Iraqi troops in northern Iraq, a Pentagon spokesman said.
If confirmed, it would be the first recorded chemical attack on US troops since the Islamic State overran parts of northern and western Iraq in 2014.
According to Navy Captain Jeff Davis, only one of the shells lobbed at Qayyarah Airfield West, where US troops are based, tested positive for a mustard agent. There were no US casualties, Davis said, and the shell, "likely a rocket or mortar, was imprecise and crude".
No service members showed any signs of mustard agent exposure, Davis added. Concentrations of mustard gas can cause agonising burns and blisters, blindness and permanent disfigurement. US troops often deploy with protection against chemical weapons, including gas masks.
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