Last week, Kurdish, US and German officials claimed that Islamic State used mustard gas against Peshmerga fighters in northern Iraq.
"That is a presumptive field test and it is not conclusive, and what those results tell us is merely the presence of that chemical. It doesn't tell us anything more than that," Brig. Gen. Kevin Killea said as quoted by CNN.
He added that definitive test results will be completed “in a couple of weeks.”
Islamic State is a violent extremist group that has seized large areas in Iraq and Syria, establishing a caliphate on territories under their control.
Islamic State is being countered by Syrian and Iraqi government forces, Syrian and Iraqi Kurds, as well as a US-led international coalition. The Peshmerga, the military forces of Iraqi Kurdistan, have rolled back Islamic State gains in Iraq’s northwest.