Confirmation that the United States and Iran are engaged in conversations about IS (also known as ISIL or ISIS) comes amid reports that Iran has launched air strikes against IS targets in Iraq, a move that has led to speculation that the Obama administration and Tehran are coordinating more closely than first thought.

Asked on Wednesday to reveal the last time the United States and Iran had any sort of discussions about the anti-IS fight, Harf confirmed that such conversations had taken place “on the sidelines” in Vienna.

“That’s the only place we have raised it,” Harf said during the State Department’s daily brief. “I’m guessing—I’m assuming it came up during the last round we had.”

The issue of U.S. operations against IS “frequently” comes up between U.S. officials and Iranian ones during the nuclear talks, Harf said.