UPDATE 1-Russia mourns victims of deadly concert hall attack

Russia lowered flags to half-mast on Sunday for a day of mourning after scores of people were gunned down with automatic weapons at a rock concert outside Moscow in the deadliest attack inside Russia for two decades. President Vladimir Putin declared a national day of mourning after pledging to track down and punish all those behind the attack, in which 133 people were killed, including three children, and more than 150 injured.