At 18:00 on Friday evening, the alarm was raised about a shooting in the concert hall Crocus city hall in Krasnogorsk in Moscow.
Images from social media show three armed men in camouflage clothing moving around the building.
The concert hall then caught fire and explosions are said to have been heard. The roof collapsed from the fire.
At least 60 people have died and more 145 people are injured after the shooting, which is classified by Russian authorities as a terrorist attack.
IS-Khorasan has claimed responsibility on Telegram and according to US sources.