ISIS-K: What to know about the group that claims responsibility for Moscow concert attack

A branch of the Islamic State has claimed responsibility for the deadly attack on a Moscow concert hall last week.

The group, known as ISIS-K, is primarily based in Afghanistan and Pakistan. But U.S officials warn that it is expanding its reach.

We hear more about the group and its motivations from Daniel Byman. He’s a senior fellow with the Transnational Threats Project at the Center for Strategic and International Studies and a professor at Georgetown University.