WASHINGTON—Islamic State militants likely used mustard agent against Kurdish forces in Iraq this week, senior U.S. officials said Thursday, in the first indication the militant group has obtained banned chemicals.
The officials said Islamic State could have obtained the mustard agent in Syria, whose government admitted to having large quantities in 2013 when it agreed to give up its chemical-weapons arsenal.
The use of mustard agent would mark an upgrade in Islamic State’s battlefield capabilities, and a worrisome one given U.S. intelligence fears about hidden caches of chemical weapons in Syria, where Islamic State controls wide swaths of territory.
It raises new questions about the evolving threat posed by Islamic State and the ability of U.S. allies on the ground to combat it. Frontline Kurdish, Iraqi and moderate Syrian forces say they aren’t getting enough U.S. support now to counter Islamic State’s conventional capabilities.
Officials say these forces may need specialized equipment and training to help protect them against unconventional weapons if they become a fixture on the battlefield.
U.S. intelligence agencies thought Islamic State had at least a small supply of mustard agent even before this week’s clash with Iraqi Kurdish fighters, known as the Peshmerga, U.S. officials said. That intelligence assessment hadn’t been made public.
The attack in question took place late Wednesday, about 40 miles southwest of Erbil in northern Iraq. A German Defense Ministry spokesman said about 60 Peshmerga fighters, who help protect Kurdish areas in northern Iraq, were reported to have suffered injuries to their throats consistent with a chemical attack while fighting Islamic State.
Mustard agent, first employed as a weapon in World War I, can cause painful burns and blisters, immobilizing those affected by it, but it is usually deadly only if used in large quantities.
“These were apparently chemical weapons. What it was exactly we don’t know,” the German ministry spokesman said, adding that experts were on their way to the scene to conduct a fuller analysis. He said German personnel weren’t present at the scene of the attack.
The possibility that Islamic State obtained the agent in Syria “makes the most sense,” said one senior U.S. official. It is also possible that Islamic State obtained the mustard agent in Iraq, officials said, possibly from old stockpiles that belonged to Saddam Hussein and weren’t destroyed.
U.S. intelligence agencies are still investigating the source and how it could have been delivered this week on the battlefield, officials said.
Islamic State has taken control of territory in Syria close to where President Bashar al-Assad’s forces stored chemical weapons, including mustard agent. The regime said in 2013 that all of its mustard stockpiles had been destroyed, either by Syrian forces themselves or by international inspectors.
Inspectors, however, have subsequently said they weren’t able to verify claims by the Syrian government that it had burned hundreds of tons of mustard agent in earthen pits. U.S. intelligence agencies now say they believe Damascus hid some caches of deadly chemicals from the West, possibly including mustard.
Intelligence officials and chemical-weapons experts have expressed concerns in recent months that some of those banned chemicals could fall into the hands of Islamic State or other extremist groups.
U.S. intelligence agencies have also warned the White House that the Assad regime could use chemical agents it still has to defend its remaining strongholds if they come under siege.
In addition to mustard, the Assad regime admitted to having deadlier nerve agents, such as sarin and VX. But officials said U.S. intelligence agencies don’t have any evidence to suggest Islamic State has either sarin or VX, which would be far more lethal on the battlefield.
The intelligence agencies have said that they believed Islamic State has used chlorine gas in attacks in Iraq. Chlorine isn’t a banned chemical agent but its use as a weapon is prohibited under international law.
U.S. officials have also accused the Assad regime of using chlorine gas in attacks against opposition forces, a charge Damascus denies.
It is unclear how much mustard agent Islamic State might have obtained. A senior military official said the amounts weren’t believed to be large.
Pentagon officials sought to play down the dangers to U.S. military personnel in Iraq since they aren’t taking part in combat operations alongside Peshmerga fighters or other Iraqi forces.
“Mustard isn’t VX or sarin,” the senior U.S. military official said. “It has to be used in high concentrations to be fatal.”
Another Pentagon official said the development was worrying, especially if mustard agent is used in more attacks, because of the physical and psychological effects its use on the battlefield could have on U.S. allies.
Alistair Baskey, a White House National Security Council spokesman, said the administration is aware of the reports and is seeking additional information. “We continue to take these and all allegations of chemical weapons use very seriously,” he said.
Hamish de Bretton-Gordon, a former commanding officer of the British army’s chemical-weapons unit, said the use of mustard agent by Islamic State could give a boost to the group’s “psychological warfare campaign.”
“You mention chemical weapons, people immediately freeze and are irrational. That’s why Islamic State wants to use them,” he said. While U.S. and international forces are trained to deal with the threat, the Peshmerga, Iraqi forces and moderate Syrian rebels may not be, he added.