An Iraqi outpost with US and Australian military advisers in western Mosul was hit with an ineffective "low grade" mustard agent by Islamic State forces on Sunday, according to CBS News.

At least six Iraqis were treated for breathing issues at a field clinic, while none of the advisers were believed to have been injured.

The Pentagon released a statement saying that the ineffective attack "further displays the desperation of ISIS as they seek to hold an untenable position in Mosul," ABC Australia reported.

"My advice right at the moment is no Australian troops were affected but Australian forces did provide assistance following the attack, said Australian Prime Minister Malcolm Turnbull. "That's my current advice received in last few minutes."

US defense officials in Iraq could not be reached for comment.

This was reportedly the second chemical attack in recent days — an Iraqi military officer also claimed that ISIS forces launched a rocket loaded with chlorine in the al-Abar district in West Mosul, one Associated Press report said.

This wouldn't be the first time ISIS militants were reportedly using chemical agents to fend off coalition fighters. Troops embedded with the Kurdish forces also reported that ISIS was using chemicals in their mortar attacks, judging by the coloration of its plumes of smoke.

Mosul, the second-largest city in Iraq, has seen heavy action since Iraqi Security Forces launched their campaign earlier this year to liberate the ISIS-controlled city.

Since then, ISF troops, backed by the coalition forces, have managed to reclaim the sparsely populated areas of eastern Mosul, however, the battle to retake western Mosul still rages on — with large portions of it requiring door-to-door combat. Some reports claim that more than half of western Mosul has been liberated.

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