WASHINGTON -- An Islamic State group rocket launched at American troops on a base in northern Iraq last week did not contain mustard agent, a U.S. military spokesman announced Tuesday, reversing the Pentagon's initial assessment of the attack.
"Definitive lab tests conclude: No mustard agent present in munitions fired at Qayyarah West Air Base Sept. 20," Air Force Col. John Dorrian wrote Tuesday in a social media statement. Dorrian is the Baghdad-based spokesman for the U.S.-led Operation Inherent Resolve coalition.
Nonetheless, American and Iraqi troops at the logistics and air hub about 40 miles south of Mosul remain on alert for the Islamic State group's potential use of such crude chemical weapons, another U.S. military spokesman said.
The militants have used a home-brewed version of mustard agent against Iraqi security forces and Kurdish Peshmerga fighters "many times" in the past two years, said Navy Capt. Jeff Davis, a Pentagon spokesman. It is likely the group at some point will turn the chemical weapons on American troops, especially as the assault on Mosul, the group's final urban stronghold in Iraq, nears, he added.
"They are dead set on it," Davis said. "They would love to use chemical weapons against us and against the Iraqis as they move forward, and we are making every effort to make sure we are ready for it."
U.S. servicemembers receive extensive training on defending against and responding to chemical weapons attacks before deploying into combat zones, Davis said. All of the "hundreds" of troops at Qayyarah West have standard gas masks and full-body protective gear.
The Pentagon has been training Iraqi troops to respond to chemical weapons as part of its train, advise and assist mission, and the U.S. military has provided the Iraqis with more than 50,000 gas masks.
Though the mustard agent that has previously been used by the Islamic State group has sickened some Iraqis in past attacks, it is not the lethal sulfur mustard gas that was used in World War I. The terrorist group's mustard agent is typically found in a powdered form and stuck to munitions with oil, Davis said. It can cause skin irritation if a person is exposed to it, but it is not a "militarily significant" chemical weapon. However, its use is illegal under international military law.
The Islamic State group's resolve to develop such chemical weapons and use it, Davis said, is "further evidence that [the Islamic State group] knows no boundaries when it comes to conduct on the battlefield."
There is no evidence the terrorist group possesses or has the means to develop more sophisticated chemical weapons, Davis said.
U.S. officials have said the Islamic State group has regularly launched rocket and mortar fire at Qayyarah West Air Base, but no American troops have been injured in any of the attacks. A fragment of a rocket that landed at the base Sept. 20 contained an oily residue that initially tested positive for mustard agent, defense officials said previously. Follow-up tests at the base were inconclusive.
On Sept. 22, Marine Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, told the Senate Armed Services Committee that the military had assessed the rocket to contain "a sulfur mustard blister agent" and called it a "concerning development." Dunford's testimony was based on the initial evaluation of the substance, an official said.
Definitive testing results were not available until Tuesday, according to Dorrian's statement. It said two separate laboratories determined the rocket did not contain mustard agent.
"Results from both labs were conclusive in their findings that no chemical warfare agents were present in the munitions," the statement read.