President Vladimir Putin declared a national day of mourning after pledging to track down and punish all those behind the attack, which left 133 people dead, including three children, and more than 150 were injured.

The Islamic State claimed responsibility for Friday's attack.

People laid flowers at Crocus City Hall, the 6,200-seat concert hall outside Moscow where four armed men burst in on Friday and fired their automatic weapons in short bursts at terrified civilians.

Long lines formed in Moscow on Saturday to donate blood.

In the southwestern city of Voronezh, people were laying flowers and lighting candles at a monument to children who died there in a World War Two bombing, in solidarity with those who died in the attack near Moscow.