Chemical weapons experts have confirmed that mustard gas was used in a Syrian town where Islamic State insurgents were battling another group in August.
Traces of sulfur mustard gas were reportedly found in mortars used by Islamic State fighters, and another possible chemical weapons attack was reported last week in Syria.
Kurdish officials said their forces were attacked on Tuesday in Iraq. Around 60 fighters reportedly suffered breathing difficulties after the incident, while the US described the accounts as "plausible."
A report cites an unnamed Libyan military official as saying militias have captured a cache of Qaddafi-era chemical weapons, including mustard gas and the nerve agent Sarin.
The Pentagon once said that fewer than twenty service members were thought to have come in contact with mustard gas and the nerve agent serin.