Beirut, Lebanon - The Islamic State group claimed responsibility for a gun attack on a Moscow concert hall on Friday, which Russian authorities said killed at least 40 people.

IS fighters "attacked a large gathering... on the outskirts of the Russian capital Moscow", the group said in a statement on the Telegram messaging app.

The IS statement said the attackers had "retreated to their bases safely."

Russia's National Guard said it was on the scene and looking for the perpetrators.

Gunmen opened fire at a rock concert at Crocus City Hall in a northern Moscow suburb, killing at least 40 people, wounding 100, and setting off an inferno in the theater, authorities said.

Attackers dressed in camouflage uniforms entered the building, opened fire, and threw a grenade or incendiary bomb, according to a journalist for the RIA Novosti news agency at the scene.

Russian authorities said a "terrorist" investigation had been started, and President Vladimir Putin was receiving "constant" updates, his spokesman Dmitry Peskov told Russian news agencies.