Islamic State jihadists are accusing Kurdish Peshmerga forces of using “poisonous gas” to execute civilians in Iraq’s second largest city of Mosul.

The Kurdish Peshmerga soldiers, who have been fighting the Islamic State (IS, ISIS, or ISIL) on the ground in Iraq and Syria, have denied the allegations.

“Secular Kurdish Peshmerga militias bombard the Muslims in Mosul with American poison gases…which led to killing dozens of Muslims by suffocation and injuring dozens,” said ISIS in a statement issued by its Ninevah media wing, the International Business Times (IBT) reported.

“In an outrageous new aggression by the secular Crusader Coalition against the Muslims, the Kurdish Peshmerga militias bombarded the Muslims this evening with poison gas in ‘Uraybi and Islah Al-Zira’ei Districts, which led to killing dozens of Muslims by suffocation and injuring dozens; and there is no Strength, except with Allah Almighty,” the statement, released in English and Arabic, continued.

ISIS did not say how many civilians were allegedly poisoned.

A Twitter account linked to the Peshmerga stated that “it was ISIS which bombed the water project in Mosul with chlorine gas and is now accusing the Peshmerga,” reported IBT.

IBT was unable to independently verify which side was telling the truth.

ISIS made the accusations after the Kurdish Peshmerga forces launched an offensive against the jihadist group in Mosul, the group’s de facto headquarters in Iraq.

For the first time since they were driven out of Mosul, the Kurdish Peshmerga forces have attacked ISIS targets in Iraq’s second-largest city.

A day after ISIS accused them of killing civilians, the Iraqi Kurdish forces were credited with playing a major role in liberating the Syrian town of Kobani from the jihadist group.

Kurdish forces from Iraq and Syria backed by the U.S.-led coalition drove ISIS out of Kobani on Monday.

Last year, ISIS allegedly used chemical weapons to kill Kurdish fighters who were fighting to defend Kobani, which lies along the Turkish border.

The United Nations’ Human Rights Office recently confirmed that ISIS is showing a “monstrous disregard for human life” in the areas it has conquered, which include large swathes of Iraq and Syria.