United States and German officials have said they are looking to investigate reports that the Islamic State of Iraq and the Levant(ISIL) group used mustard gas against Kurdish fighters in Iraq.
A German defence ministry spokesperson said Berlin had "indications" there was an attack with chemical weapons this week against the Kurdish armed forces, known as the Peshmerga, that left many suffering from "respiratory irritation".
The defence ministry on Thursday said that Iraqi and US specialists were on their way to the scene of the attack to investigate, the AFP news agency reported.
A US official told the agency that the allegations were "plausible".
The statements follow claims by Kurdish officials that a chemical attack took place and wounded scores of fighters.
"Last Tuesday afternoon, Peshmerga forces in the Makhmur area 50km west of the city of Arbil were attacked with Katyusha rockets filled with chlorine," a senior Peshmerga official told the AFP.
In March, the autonomous Kurdish government in northern Iraq said it had evidence that ISIL used chlorine in a car bomb attack on January 23.
The Pentagon on Thursday said it was "seeking additional information" about the latest alleged attack.
"We continue to take these and all allegations of chemical weapons use very seriously," said Pentagon spokesman Navy Captain Jeff Davis.
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According to the Wall Street Journal, German officials said approximately 60 Iraqi Kurd fighters reportedly "suffered injuries to their throats consistent with a chemical attack while fighting [ISIL]".
The paper said US officials confirmed that mustard gas was likely used.
On Thursday, Samantha Power, the US representative to the UN said she was not in a position to confirm the report.
If the allegations are true, she added, "it would be a further testament of the hideous nature of ISIL as a movement and its utterly brutal approach to what it calls warfare, but what really appears to be systematic attacks on civilians".
Mustard gas is an asphyxiant that has been banned in war by the UN since 1993.
Kurdish fighters have been battling ISIL in both Syria and Iraq, as the US-led coalition continue to bombard positions belonging to the armed group.
The Wall Street Journal said that ISIL could have obtained the chemical weapons in Syria.
The Syrian government of Bashar al-Assad used chemical weapons a number of times in rebel-held strongholds during the conflict in the country that began in 2011, according to the UN and international human rights organisations.
In 2013, Damascus greed to give up its chemical arms and said all stockpiles were destroyed. UN inspectors were never able to confirm the claims.