ARBIL, Iraq - Iraqi Kurdish authorities said on Saturday they had evidence that Islamic State had used chlorine gas as a chemical weapon against their peshmerga fighters in northern Iraq in January.
The Security Council of the semi-autonomous Kurdish region said in a statement to Reuters that the peshmerga had taken soil and clothing samples after an Islamic State car bombing attempt on Jan. 23.
It said laboratory analysis showed "the samples contained levels of chlorine that suggested the substance was used in weaponized form." The Kurdish allegation could not be independently confirmed.
Chlorine is a choking agent whose use as a chemical weapon dates back to World War One. It is banned under the 1997 Chemical Weapons Convention, which prohibits all use of toxic agents on the battlefield.
Peter Sawczak, spokesman for the Dutch-based Organisation for the Prohibition of Chemical Weapons, said: "We have not had a request from Iraq to investigate claims of use of chemical weapons in Iraq, and the OPCW cannot immediately verify the claims."
Chlorine has been used "systematically" in the civil war in neighbouring Syria, an OPCW fact-finding mission found last year. The OPCW would have to get its own samples to confirm the use of chemical weapons in a member state.
The Kurdish statement said the car bombing attempt happened on a highway between Mosul and the Syrian border. A Kurdish security source said that the peshmerga fired a rocket at the car carrying the bomb so there were no casualties, except for the suicide bomber.
About a dozen peshmerga fighters experienced symptoms of nausea, vomiting, dizziness or weakness, the source said.
The statement said the analysis was carried out in a European Union-certified laboratory after the soil and samples were sent by the Kurdish Regional Government to a "partner nation" in the US-led coalition that is fighting Islamic State militants in Iraq and Syria.
The source described the samples as "leftovers from the suicide bomber", but declined to identify the laboratory.
The White House said in a statement it could not confirm the allegations but found them "deeply disturbing" and was monitoring the situation "very closely."
A US defence official said the use of chlorine as a weapon was a possible sign of "growing desperation due to the pressure being applied by coalition air power and Iraqi ground forces."
Iraq's Kurds were the victims of the deadliest chemical attack of modern times when Saddam Hussein's air force bombed the town of Halabja in 1988, gassing at least 5,000 people to death.