Vladimir Putin announces March 24 as national mourning day, calls Moscow concert hall attack 'barbaric'

Russian President Vladimir Putin on Saturday called an attack on a concert hall that killed more than 100 a "barbaric terrorist act" and announced a day of national mourning.

In a televised address to the nation, Putin said: "I am speaking to you today in connection with the bloody, barbaric terrorist act, the victims of which were dozens of innocent, peaceful people. ... I declare 24 March a day of national mourning."

Russian President Putin also said Saturday that the four gunmen who killed more than 100 at a Moscow concert hall had been arrested, and vowed harsh retribution for everybody involved in plotting the attack.

"All four perpetrators of the terrorist act who shot and killed people have been detained. They were travelling towards Ukraine ... We will identify and punish everybody who stood behind the terrorists, who prepared the attack."