Germany's foreign intelligence agency BND has collected evidence of mustard gas use by the Islamic State group.
German daily Bild reported Monday that BND intelligence agents collected blood samples from Kurds who were injured in clashes with IS.
It quoted BND chief Gerhard Schindler as saying that the agency has "information that IS used mustard gas in northern Iraq."
Schindler told the paper that the mustard gas either came from old Iraqi stockpiles produced under Saddam Hussein's rule or was manufactured by IS after it seized the University of Mosul.
A senior German intelligence official, speaking on condition of anonymity because he wasn't authorized to discuss the matter publicly, confirmed the comments attributed to Schindler. He declined to confirm that the BND collected blood samples or discuss the agency's methods.
U.S. Defence Department spokeswoman Cmdr. Elissa Smith said "while we will not comment on intelligence or operational matters, let us be clear: any use by any party ... of a chemical as a weapon of any kind is an abhorrent act.
"Given the alleged behaviour of ISIL and other such groups in the region, any such flagrant disregard for international standards and norms is reprehensible," Smith said, using an alternative name for the militant group.
Activists said last month that IS attacked the northern Syrian town of Marea with poisonous gas although it was not clear if chemical weapons were used.
Doctors Without Borders said that four patients exhibiting symptoms of exposure to chemical agents were treated at a hospital run by international medical organization in northern Syria on Aug. 21. It said the parents and their two daughters, arrived at a hospital run by the group one hour after the attack, suffering from respiratory difficulties, inflamed skin, red eyes, and conjunctivitis and their conditions worsened later.
The Britain-based Syrian Observatory for Human Rights and Turkey-based activist Abu al-Hassan Marea said it wasn't independently confirmed if the attack was with chemical agents.