Shell that hit Iraqi base contained sulfur-mustard agent

American troops in Iraq. File

ISIS took over Mosul, Iraq's second largest city, in the summer of 2014.

Officials have said no US troops were injured in the attempted attack.

American troops in Iraq.

If the White House approves, these troops will stay at an area just south of Mosul that the US has established as a hub called "Q-West" since it is located west of Qayara.

Iraq's army is focusing on cutting off Islamic State of Iraq and Levant's (ISIL's) supply lines as USA advisers on the ground assist the Iraqis and the Kurdish peshmerga in preparing for an assault on Mosul.

The U.S. government has previously accused the Islamic State of using chemical weapons.

"We assess it to be a sulfur-mustard blister agent", Marine Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, told the Senate Armed Services Committee Thursday.

Earlier this week a rocket with a chemical agent believed to have been launched by IS landed near USA and Iraqi troops stationed at Qayyarah air base.

Once the push is launched, a coalition of heterogenous and sometimes rival Iraqi forces will have to fight through IS defences - in some cases over distances of dozens of kilometres (miles) from their current positions - to reach the city.

USA troops involved in the incident went through decontamination showers as a precaution.

USA Today reported that although American forces were hundreds of yards away from the area in which the shell landed on Tuesday, and no us troops were injured in the attack, the use of chemical weapons and the possible targeting of us personnel has emerged as a concern.

Tuesday's attack comes almost three months after a top Kurdish commander in northern Iraq said that the Islamic State was stepping up its chemical weapons attacks in his region.

The Pentagon is seeking to send another 500 USA troops to Iraq, in addition to the 400 that arrived over the Labor Day weekend, two military officials tell Fox News - a development that comes amid a new wave of attacks.

"The idea is to isolate Mosul, cut it off, kill it", a senior U.S. Central Command officer told Politico.

Iraqi forces have been gearing up for a major offensive to retake the city from Qayyarah, backed by the US.

Brett McGurk, speaking at a meeting on the sidelines of the annual United Nations gathering of world leaders, said the coalition was already taking steps to ensure there would be no repeat of the abuses seen in the wake of the recapture of Iraq's Falluja in June, when Shi'ite militias detained, abused and tortured scores of Sunni civilians.

The rocket attack comes after the U.S-led coalition recently bombed a building believed to be a chemical weapons making facility near Mosul.

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