What we know about the Moscow concert hall attack — and why ISIS-K is claiming responsibility

At least 133 people were killed and more than 145 were injured on Friday in an attack after a group of armed individuals opened fire at the Crocus City Hall music venue near Moscow, Russian state media agency TASS reported, citing the Russian Investigative Committee.

The number of reported casualties would make this one of the deadliest attacks near Russia's capital in recent years.

Here's what we know so far:

A group of unidentified individuals opened fire at the Crocus City Hall, a music venue located on the western edge of Moscow, on Friday evening.