Iraqi Shiite men who have volunteered to join government forces and militias in the fight against Islamic State, take part in a training session in Hillah on October 18

US security officials said Thursday that they were looking into a new report that Islamic State militants had used chlorine gas as a weapon against Iraqi police officers last month near Balad, north of Baghdad.According to the accounts of the officers, fighters for the Islamic State set off an explosive that unleashed a mass of yellow smoke that hung close to the ground, The Washington Post reported. The Post said hospital officials who treated the men, as well as an unnamed Iraqi Defense Ministry official, confirmed the men's suspicion that chlorine gas had been used against them. Eleven officers were made ill, though all survived.Unconfirmed reports of improvised bombs made with chlorine gas and used by militants have arisen from time to time since Islamic State began seizing territory in Iraq at the beginning of the year, raising concerns that Iraq's old chemical weapons stores had fallen into the militants' hands.A spokesman for the National Security Council, Alistair Baskey, said US officials were examining the new report."We continue to take all allegations of CW use - and in particular these recent allegations regarding the use of chlorine as a chemical weapon - very seriously," he said. "We are aware of the reports but cannot confirm details and are seeking additional information. The use of chlorine as a chemical weapon is an abhorrent act. These recent allegations underscore the importance of our work to eliminate chemical weapons in this volatile region."The Organization for the Prohibition of Chemical Weapons noted in September that chlorine gas was being used in parts of the conflict in Syria, where the Islamic State is also fighting. The United States has attributed those attacks to the government of President Bashar Assad.If the new report is confirmed, the use of chlorine gas by Islamic State would be the latest iteration of a weapon that has been employed by Iraq's Sunni militants since the years after the US invasion in 2003.During the 2000s, the weapons were used intermittently in attacks against US and Iraqi forces and against civilians. In early 2007, there appeared to be a flurry of such attacks, mainly in Anbar province, where US and Iraqi forces were trying to wrest control of territory from al-Qaida in Iraq, also known as al-Qaida in Mesopotamia.The crude bombs were often made by mixing conventional explosives with cylinders of chlorine compounds usually used for water purification. Sometimes insurgents would pack explosives on chlorine tanker trucks, or on dump trucks full of chlorine, turning the vehicles into giant, mobile bombs.These bombs were often ineffective as chemical weapons, and wounds that resulted from their use were most often related to the shrapnel from the conventional explosive used to try to disperse the chlorine, according to US service members who encountered the weapons during their tours.At times, however, the chlorine was distributed in harmful ways, irritating airways and eyes and causing burns. In the worst cases, Iraqi civilians and US troops suffered inhalation injuries. This type of wound received enough attention in the US military that the Navy came to recognize injuries caused by chlorine gas and explosives as worthy of a Purple Heart, the medal awarded for battlefield wounds.

© 2014, The New York Times News Service