ISIL used chlorine gas against security forces and Shia armed fighters last month in a battle north of Baghdad, Iraqi officials said on Friday.

If confirmed, the officials’ statements would mark the first time the Islamic State of Iraq and the Levant (ISIL) attempted to use chlorine since its blitz earlier this year that seized large chunks of territory in northern Iraq and neighboring Syria.

Three Iraqi officials — a senior security official, a local official from the northwestern town of Duluiya and an official from the nearby town of Balad — told The Associated Press that ISIL used bombs with chlorine-filled cylinders during clashes in late September in the two towns.

The group failed to capture both towns.

In the attacks, about 40 troops and Shia armed fighters were slightly affected by the chlorine, showing symptoms consistent with chlorine poisoning, such as difficulty in breathing and coughing, the three officials said. The troops were treated in hospital and quickly recovered.

The senior security official said it was most likely that the ISIL fighters obtained the chlorine from water purification plants located in the areas they had overrun earlier. Iraqi intelligence has indicated that ISIL has some shells filled with chlorine and they are ready to be used, the official also said.

"The [ISIL] fighters seized some quantities of chlorine after seizing control of some water purification plants or sites where chlorine was kept," said the senior official, adding that ISIL "has some experts who were able to manufacture chlorine shells."

The three officials, who spoke on condition of anonymity because they were not authorized to speak to media, did not elaborate or provide more details. The use of chlorine by the ISIL in Iraq in September was first reported by the Washington Post, which said the instance appeared to be the first chlorine attack used by ISIL in battle.

The Post also reported that Iraqi forces mentioned two other chlorine attacks by ISIL since the summer, but that the details of those incidents remain unclear.

Chlorine, a chemical used in industry and water purification process, was first introduced as a chemical weapon in World War I.

In Syria, a joint U.N. fact-finding mission sent to investigate alleged chlorine attacks was ambushed and briefly detained by armed men earlier this year in rebel-held territory. The mission had said it was virtually certain chlorine had been used as a chemical weapon in the country's north.

Syrian President Bashar al-Assad had agreed with the United States and Russia to dispose of his chemical weapons — an arsenal that Damascus had never previously acknowledged — after hundreds of people were killed in a sarin gas attack on the outskirts of the capital, Damascus, in the summer of 2013. But chlorine was not listed as part of the Syrian arsenal.

Chlorine gas, when inhaled, swallowed or exposed to through skin causes difficulty in breathing, coughing and eye and skin irritation. It is not as toxic or effective at killing as sarin, a nerve agent, and experts say it is difficult to achieve high concentrations of chlorine by dropping it from the air.

Al Jazeera and The Associated Press