There is growing evidence ISIS is using chemical weapons.
Speaking to the BBC, an anonymous U.S. official says ISIS is both making and using mustard gas in Iraq and Syria.
According to the source, ISIS has a chemical weapon research team working on ways to more effectively use the deadly agents.
That accusation adds to a growing list of claims that ISIS is turning to chemical weapons in its skirmishes.
The BND, Germany's intelligence agency, has also reportedly found evidence of ISIS using mustard gas in northern Iraq.
In August, the Syrian American Medical Society said one of its field hospitals north of Aleppo treated civilian victims for what appeared to be a mustard gas attack perpetrated by ISIS.
And then there's the Syrian regime, which agreed to destroy its chemical weapon stockpile in 2013. (Video via Presidency of the Syrian Arab Republic)
The United Nations voted to investigate recent chemical attacks in Syria with the Organization for the Prohibition of Chemical Weapons in August.
It's unlikely the U.N. would be able to enforce international chemical weapons law against ISIS.
This video includes images from Getty Images.