Special to WorldTribune.com

Islamic State of Iraq and Levant (ISIL) used mustard gas in an attack in Hasakah, Syria, U.S. investigators have confirmed.

The U.S. is still investigating the amount and sophistication of how the agent was delivered, according to a CNN report.

Investigators are also examining samples from an ISIL attack this past week near the town of Makhmour in northern Iraq, a U.S. official said.

The Kurdish Peshmerga believe ISIL used mortar shells carrying a chemical agent in the attack on Makhmour. Field commander Brig. Gen. Sirwan Barzani told CNN the coalition official who originally took samples from his men of the chemical substance they were exposed to has called him back to say the samples have been tested and show mustard, but U.S. officials said nothing has been concluded.

The U.S. officials said the amount of mustard gas used in the attack in Syria is thought to be small and the concentration low. An official told CNN the mustard agent used in Hasakah is more likely precursor chemicals, rather than a complex munition, a sign this did not come from a cache of Syrian President Bashar Assad but was probably mixed by ISIL on its own.

Precursors are chemicals involved in production stages for toxic chemicals, according to the Organization for the Prohibition of Chemical Weapons (OPCW).

U.S. intelligence agencies have said in the past they believed ISIL used chlorine gas in attacks in Iraq. Chlorine is not a banned chemical agent.

  Hasakah, mustard gas, peshmerga, U.S. confirms ISIL chemical weapons strike using precursor components, WorldTribune.com