The nation’s top intelligence official confirmed Tuesday that the Islamic State has succeeded in making and deploying chemical agents in Iraq and Syria — calling it the first such attack by an extremist group in more than two decades.

The confirmation of mustard gas use came during Director of National Intelligence James Clapper’s testimony before the Senate Armed Services Committee, where he spoke to the Islamic State’s growing sophistication online and in the battlefield.

He did not elaborate on where and when the chemical attacks occurred, though there has been mounting evidence the terror group was experimenting with chemical weapons.

“[The Syrian government] has used chemicals against the opposition on multiple occasions since Syria joined the Chemical Weapons Convention. ISIL has also used toxic chemicals in Iraq and Syria, including the blister agent Sulfur mustard,” Clapper said.