Kurdish forces fighting Islamic State (IS) jihadists in northern Iraq have reported being attacked with chemical weapons, the German defence ministry said Thursday.

"We have indications that there was an attack with chemical weapons" against the peshmerga fighters that left many suffering from "respiratory irritation," a ministry spokesman told AFP.

A senior official from the peshmerga told AFP the attack happened two days ago and wounded several dozen fighters.

"Last Tuesday afternoon, peshmerga forces in the Makhmur area 50 kilometres (30 miles) west of the city of Arbil were attacked with Katyusha rockets filled with chlorine," the official said on condition of anonymity.

The defence ministry in Germany, which is providing arms and weapons training to the Kurdish forces, said that "American and Iraqi specialists from Baghdad are on their way to find out what happened".

A ministry spokesman had said earlier "there was a chemical weapons attack" near Arbil, the capital of Iraq's autonomous Kurdish region.

A second ministry spokesman later stressed that German forces were not present during the attack, but that "we have indications that there was an attack with chemical weapons".

Germany has been supporting the Kurdish peshmerga fighters since September to back their push against IS jihadists, and currently has about 90 personnel on the ground.

"German soldiers were not affected or in danger" during the reported attack, the spokesman said. "The protection of our soldiers in northern Iraq is already at the highest level."

IS has previously been accused of using chlorine against Kurdish forces in Iraq.

In March, the autonomous Kurdish government in northern Iraq said it had evidence that the jihadist group used chlorine in a car bomb attack on January 23.

Last month, the Conflict Armament Research group and Sahan Research group said IS had also targeted peshmerga with a projectile filled with an unknown chemical agent on June 21 or 22.

The chemical used had characteristics and clinical effects "consistent with a chlorine chemical agent," the groups said.

The organisations said they had also documented two such attacks against Kurdish fighters from the People's Protection Units in Syria's northeastern Hasakeh province on June 28.

It said that upon impact, the projectiles had released a yellow gas "with a strong smell of rotten onions".

There were no deaths but troops exposed to it had experienced burning of the throat, eyes and nose, severe headaches, muscle pain, impaired concentration and mobility, and vomiting.

"Although these chemical attacks appear to be test cases, we expect IS construction skills to advance rapidly as they have for other IEDS (improvised explosive devices)," said Emmanuel Deisser, managing director at Sahan Research, at the time.