Russia on Saturday said it had arrested 11 people, including four assailants, involved in the Moscow concert hall attack and reported a new death toll of 93 which it warned could rise.

Friday evening's attack, which was claimed by the Islamic State, is the deadliet in Moscow for at least a decade.

The Kremlin said the head of the FSB security service had informed President Vladimir Putin about the arrests on Saturday.

"FSB Director Alexander Bortnikov reported to the president on the detention of 11 people, including four terrorists involved in the terrorist attack at Crocus City Hall," it said in a statement.

Russia's Investigative Committee, which probes major crimes, said Saturday that at least 93 people had been killed.

"At the moment, it has been established that 93 people are dead. The death toll is expected to rise," it said in a statement published on Telegram.

It said people died both from gunshot wounds and from smoke inhalation after a fire engulfed the packed venue in Moscow's northern Krasnogorsk suburb.