Kurdish security forces gather at the site of a bomb attack in Erbil, the capital of Iraq's Kurdistan region, April 17, 2015.
Kurdish authorities said on Tuesday they suspected a rocket fired by Islamic State at their peshmerga forces in northern Iraq contained chemical substances.
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. 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 two other incidents are currently 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".