The United States believes Islamic State (ISIS) jihadists likely used mustard agent in an attack earlier this week on Kurdish forces in Iraq, senior officials said Thursday, according to The Wall Street Journal.
If true, it would be the first indication that ISIS has obtained a banned chemical weapon.
Officials said Islamic State could have obtained the mustard agent in Syria, whose government admitted to having large quantities of the blistering agent in 2013, when it agreed to give up its chemical weapons arsenal.
“That makes the most sense,” a senior U.S. official said of the possibility that Islamic State obtained the mustard in Syria.
ISIS could also have obtained the mustard agent in Iraq, officials said. U.S. intelligence agencies are still investigating the case.
The Assad regime in Syria said in 2013 that all of mustard stockpiles were destroyed, either by Syrian forces themselves or by international inspectors.
But inspectors said they were never able to verify claims by the Syrian government that it burned hundreds of tons of mustard agent in earthen pits, and U.S. intelligence agencies now say they believe Damascus hid caches of chemical agent from inspectors.
The use of mustard agent would mark a sharp upgrade in ISIS’s battlefield capabilities, and a worrisome one, noted The Wall Street Journal.
U.S. intelligence agencies have said in the past they believed Islamic State has used chlorine gas in attacks in Iraq. Chlorine, however, isn’t a banned chemical agent.
In addition to mustard, the Assad regime admitted to having deadlier nerve agents, such as sarin and VX.
In 2013, the United States threatened military intervention against Syria's government after sarin gas attacks that year killed hundreds of residents in Ghouta, a rebel-controlled suburb of the Syrian capital Damascus.
The Damascus government forestalled foreign intervention by agreeing to a U.S.- and Russian-brokered deal under which it joined the Organization for the Prohibition and Chemical Weapons (OPCW), admitting to having a chemicals weapons program and promising to eliminate it.
A joint mission between the UN and the OPCW was then tasked with eliminating Syria's chemical weapons program, and the government of President Bashar Al-Assad last year handed over 1,300 tons of chemical arms.
In May, however, diplomats said that international inspectors had found traces of sarin and VX nerve agent at a military research site in Syria that had not been declared to the OPCW.
The finding of VX and sarin supports assertions by Western governments that Assad withheld some of his stockpile, or did not disclose the full extent of Syria's chemical capability or arsenal to the OPCW.