Officials are investigating if the Islamic State used chemical weapons in a recent attack in Iraq.

The Kurdistan Regional Security Council and officials from the United States-led coalition against the Islamic State are looking into Thursday’s events, the council tweeted on Friday.

According to the council, Islamic State militants used homemade rockets in an attack on the town of Sinjar, which is located about 80 miles west of Mosul in northern Iraq.

Dozens of civilians and Peshmerga military forces subsequently vomited, experienced nausea or had trouble breathing and received treatment, the council tweeted. It did not say if anyone died.

Officials did not specify which chemical the Islamic State is believed to have used in the attack.

If the investigation does confirm a chemical weapon was used, the council said it would be the eighth time that the Islamic State used the substances in their attacks against Peshmerga forces.

The council tweeted last March that it believed the Islamic State used chlorine in a car bomb attack in Iraq in January 2015, saying soil and clothing samples contained evidence of its use.

The council has also tweeted it has evidence the Islamic State used mustard gas in prior attacks, saying some 35 Peshmerga forces were exposed during an August 2015 shelling near Erbil, Iraq.

The Organisation for the Prohibition of Chemical Weapons (OPCW) has also said it was concerned about chlorine gas being used in various attacks in Syrian villages in 2014.

An OPCW fact-finding mission into the attacks in Syria did not address who used the chlorine.

More than 190 countries have agreed to a 1997 United Nations treaty on chemical weapons, which prohibits their use or production and calls for nations to destroy their existing arsenals.