IS launches mustard gas attack on US troops
Islamic State has used chemical weapons against US troops in the first such attack on American servicemen since World War1.
The jihadists fired a rocket containing suspected mustard gas at an airbase in Qayyarah, south of Mosul, where the troops are supporting Iraqi forces.
US officials said the soldiers took decontamination showers and were not suffering symptoms of exposure.
Initial tests carried out by US forces revealed a positive result for toxic chemical agent mustard, a banned substance which can cause burns and breathing difficulties.
"It was mustard agent in a powderised form - the same thing we have seen IS use to little effect many times in Syria and Iraq," said US Navy captain Jeff Davis, a Pentagon spokesman, adding that the agent was "low grade and poorly weaponised".
"The device, likely a rocket or mortar, was imprecise and crude," he said.
The use of chemical weapons will be of great concern to ground forces as they advance towards Mosul, which was overrun by I S in 2014 and continues to be a stronghold .
Just 50km away several hundred US troops are expected to begin battle for Mosul next month.