"Nobody's been impacted significantly by this", said Martin, who spoke to reporters at the Pentagon from Iraq.

The attack came a day after an Iraqi military officer said IS militants launched a chlorine gas attack by rocket in the al-Abar neighborhood, a newly liberated area in western Mosul. "They were taken back for the appropriate level of medical care".

"We're not certain at this time exactly what the agent is", he added. "Our forces will continue the search for other suspects", it said.

Police on Sunday reported a toxic gas attack on its troops that caused no deaths.

Martin declined to give details about the incident, including whether coalition military advisers had donned chemical weapons protection suits or whether an alert had gone around afterwards to notify troops of possible chemical attacks.

ABC reported that the Iraqi military unit that was attacked had both Australian and U.S. military advisers.

"Our advisers. are with Iraqi security forces at various command and control locations throughout Iraq", he said.

"We're forward with the Iraqis, we share the same risk they do", Martin said.

U.S. Army Maj. Gen. Joseph M. Martin, commanding general of Combined Joint Forces Land Component Command-Operation Inherent Resolve and 1st Infantry Division, discusses future operations for the liberation of Mosul with Staff Lt. Gen. Abdul Amir, commanding general, Iraqi ground forces, near Bakhira, Iraq, April 13, 2017. "With that risk, there's danger, but our soldiers are prepared with the appropriate equipment".