Nepal, March 25 -- Russia lowered flags to half-mast for a day of mourning and charged four men it accused of gunning down scores of people at a concert outside Moscow on Friday night in the deadliest attack inside Russia for two decades.

President Vladimir Putin declared Sunday a national day of mourning after pledging to punish all those behind the attack, in which 137 people were killed, including three children, and 182 were injured.

Over 100 people remained in hospital, some of them in a serious condition. Video footage showed a sombre-looking Putin lighting a candle at a church at his residence outside Moscow on Sunday evening to honour those who died.

Earlier on Sunday, people laid flowers at Crocus City Hall, the 6,200-seat con...