'Credible' That ISIS Used Chemical Agent Against Kurdish Fighters

— -- The U.S. has found it credible that ISIS used a “blistering agent” earlier this week against Kurdish forces in northern Iraq, according to officials. But no determination has been made as to what type of chemical agent may have been used in the attack, which affected a small number of Kurdish fighters.

A U.S. official said the attack occurred several days ago and involved a small amount of blistering agent that affected a small number of Kurdish fighters.

It is unclear how ISIS may have obtained the undetermined chemical agent.

Mustard gas is the most well-known blistering agent, but officials cautioned that no determination had been made as to whether mustard gas was used.

They noted that there are many kinds of blistering agents that cause similar skin reactions to those seen in the attack.

A statement from the German Defense Ministry said that as many as 60 Kurdish fighters had suffered breathing problems as a result of the new attack. The German military is helping to train Kurdish forces in northern Iraq to fight ISIS.

The U.S. official said this latest incident is believed to be credible based on the attack a few days ago, though no final determination has been made.

Over the past year the U.S. has determined that ISIS has used crude weapons carrying chlorine for some attacks in Iraq. Chlorine is not designated a chemical weapon because it is also used for civilian purposes.