Iraqi Kurdish authorities said on Saturday they had evidence that Islamic State had used chlorine gas as a chemical weapon against their peshmerga fighters.

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 suicide bombing in northern Iraq in January. It said laboratory analysis showed “the samples contained levels of chlorine that suggested the substance was used in weaponised form.”

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. […]