ERBIL, Iraq — Kurdish authorities said on Tuesday they suspected a homemade rocket fired by ISIS at their peshmerga forces in northern Iraq contained chemical substances, accusing the terrorists of an increasing use of chemical weapons.

The Kurdistan Region’s Security Council (KRSC) said the attack had taken place along the front line north of Mosul on Aug. 31, and one peshmerga fighter was receiving treatment in hospital.

A “considerable amount” of yellow smoke was produced, it said.

Samples taken from the site of another attack earlier this year tested positive for chlorine, and at least two other incidents are being investigated.

“This is one of an increasing number of attacks in recent months suspected of carrying chemical substances,” the KRSC said in a statement.

“We remain deeply concerned with the escalation and delivery method of these attacks, and urgently call on the International Coalition to provide protective equipment to peshmerga forces,” it said, referring to the foreign powers, led by the United States, supporting the fight against ISIS.

The Organization for the Prohibition of Chemical Weapons in The Hague has expressed its concern about the alleged use of chemical weapons in the region but has said either Baghdad or the U.N. Security Council would have to make a request if the OPCW were to investigate.