What We Know About ISIS-K, Alleged Perpetrators of Moscow Concert Hall Massacre

As questions remain about whether the group was behind the attack, here is what you need to know about ISIS-K.

A file photo shows the ISIS terrorist group's flap. Hussein Malla/AP Photo

At least 133 people died in a massacre at a concert hall in Moscow on the night of March 22 in what was the deadliest terror attack on Russian soil in more than a decade. ISIS-Khorasan (ISIS-K), a terrorist group based in Afghanistan, claimed responsibility for the carnage.

The ISIS branch claimed responsibility for the massacre in a statement posted on affiliated social media channels, although neither the Kremlin nor Russian security services have officially assigned blame for the attack.