USA trying to identify chemical agent used in Mosul attack

The chemical attack by ISIS is the second of its kind over the last few days as Iraq forces struggle to liberate the denser western side of Mosul.

IS has periodically carried out attacks using chemical weapons, but both the toll and the impact on military operations has been minimal and the jihadists' bombs and bullets are far deadlier.

Twenty five Iraqi soldiers required medical treatment after their unit was hit with a mustard agent fired from an ISIS rocket on Sunday, according to CBS News.

"These jihadists had infiltrated into areas recently captured by the Iraqi Security Forces", the ISF said in a statement. The last one occurred Saturday when ISIS launched an attack with a gas agent in western Mosul.

Progress has slowed considerably in Mosul because much of the fighting is now door-to-door.

Asked if he was saying no USA or Australian forces had been exposed to chemicals, Martin said: "We have not confirmed exposure at this time".

If there is a siege and hundreds of thousands of people don't have water and don't have food, they will be at enormous risk.

More than 327,000 have fled fighting since the offensive operation started on October 17, with strong air and ground support from a US -led coalition.

Government forces, including army, police and elite counter terrorism units have taken back most of it, including the half that lies east of the Tigris river. Wilson said that in the past, IS has demonstrated a "low-grade capability" with chemical weapons.