By Isabel Coles ARBIL, Iraq (Reuters) - Iraqi Kurdish authorities said on Saturday they had evidence that Islamic State had used chlorine gas as a chemical ****** against their peshmerga fighters in **rthern Iraq in January. The Security Council of the semi-auto**mous 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. chlorine is a choking agent whose use as a chemical ****** dates back to World War One. It is banned under the 1997 Chemical ******* Convention, which prohibits all use of toxic agents on the battlefield.