The attack began when gunmen donning combat gear burst into Crocus City Hall, where concertgoers were gathering to hear the Russian band Picnic, and opened fire.

The gunmen also threw explosives inside the concert hall during the attack, which set the building on fire, Russian media reported.

People were being evacuated, but some remained trapped inside the burning building, Russian media said.

Russian Rosguardia (National Guard) servicemen responding to the scene of the attack.

The Islamic State made the claim on its affiliated social media channels, although Fox News Digital has not been able to independently verify it.

Before ISIS claimed responsibility, Russian officials said the incident was being investigated as a terrorist attack.

Gunmen opened fire inside the building and dropped explosives that set it on fire, according to Russian media.

Russia's Investigative Committee said it has opened a criminal probe into the attack.

Russian Culture Ministry has canceled all mass and entertainment events in the coming days in the area.