Military officials have begun testing shell fragments for possible chemical agents after ISIS used mustard gas during attacks in recent months.
An official said: “Given [ISIS’] reprehensible behaviour and flagrant disregard for international standards and norms, this event is not surprising.”
But Washington does not believe the barbaric sect has been successful in developing lethal chemical weapons, stating that more conventional weapons are the biggest threat to Iraqi and Kurdish forces as they attempt to retake the city.
Soldiers have been photographed using gas masks as they prepare for the eventuality that the terror cult resorts to underhand tactics.
ISIS fighters have been bombarded in the past two days in its Iraqi stronghold, losing more than than 75 square miles of territory since the offensive began.
It has been estimated around 1million civilians are still in Mosul, which was captured by Daesh two years ago.
Barack Obama said: “If we aren”t successful in helping ordinary people as they”re fleeing from ISIL, then that makes us vulnerable to seeing ISIL return.”
The International Organisation for Migration’s Iraq chief, Thomas Weiss, said on Tuesday he expected militants to use Mosul residents as human shields.
He said: “We also fear, and there has been some evidence that ISIL might be using chemical weapons. Children, the elderly, disabled, will be particularly vulnerable.”
Former CIA officer Colonel Peter Mansoor added: ”The result is inevitable. The Iraqi forces with the help of US air support will end up crushing ISIS but it will be a hard fight for that to happen.
“The enemy has had more than two years to dig into the urban landscape. He”s lighting on fire pools of oil to darken the skies and make it harder to target him.”
Leader of the warmongering group Abu Bakr al-Baghdadi is said to be trapped in the besieged city.
It is believed the jihadi is joined by ISIS bomb maker Fawzi Ali Nouimeh – leading the fears ISIS are prepared to fight to the bitter death to protect the city.