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.

This article was originally published on WBUR.org.

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