- Russian President Vladimir Putin on Saturday called Friday's attack on a concert hall in Moscow a "barbaric terrorist act" and declared a day of national mourning on March 24.

- Putin said all four direct perpetrators of the terrorist attack were detained, and vowed harsh retribution for everybody involved in plotting the attack.

- The death toll in the attack has risen to more than 130, local media reported, citing the Russian Investigative Committee.

- Russian authorities have initiated a criminal investigation into the attack, which the Islamic State group claimed it had carried out.