The Islamic State (ISIS) has claimed responsibility for a shooting at the Crocus City Hall in Moscow, the Russian capital.
At the time of the attack on Friday night, the death toll stood at 40.
The number of fatalities has now risen to at least 60, including children, according to Russian state news agency RIA.
No fewer than 145 persons were injured in the attack while the death toll is expected to rise.
The terror group took responsibility for the attack in a short statement published by ISIS-affiliated news agency Amaq on Telegram but did not provide evidence to support the claim.
RIA said the attackers who showed up in camouflage and without masks allegedly fled in a white car that had a Renault symbol with a tinted rear window.
Before they fled, they sprayed bullets from automatic weapons on the people at the concert and threw a grenade, setting the hall on fire.
The roof of the concert hall was said to have partially collapsed.
The Investigative Committee of Russia and the operational units of the ministry of internal affairs said they are investigating the potential terrorist attack.