WASHINGTON, D.C.: Islamic State militants allegedly used deadly mustard gas against Kurdish forces in Iraq this week, according to media reports Thursday that cited unnamed U.S. officials. The Wall Street Journal and NBC News reported the allegations, citing unnamed defense and intelligence officials, about the Islamic State, also known as ISIL or ISIS. The Islamic State was previously accused of using chlorine gas in weapons. Mustard gas is a deadly agent that was used extensively in World War I, causing blisters on the skin and lungs. The chemical could be disbursed with artillery shells or rockets.