Russian security forces launched a massive hunt on Saturday for perpetrators of a bomb attack on the Moscow metro that killed at least 39 people as the city's mayor warned the final death toll could rise.

President Vladimir Putin blamed Chechen separatists for Friday morning's rush-hour bombing that tore through the second carriage of a packed train.

Police said 105 people were still in hospital, many suffering carbon monoxide poisoning as well as broken limbs and severe burns. More than 400 people showed up to donate blood for the victims.

The Mayor of Moscow Yuri Luzhkov said the number of people killed in the explosion looks set to rise.

"Unfortunately the number of victims of the terrorist attack may still rise, since 14 people in city hospitals were critically injured in the attack and a further 24 were seriously hurt," Luzhkov told reporters.

He has declared Monday a day of mourning when the first burials are due to take place.

Muscovites grieved for the victims of the blast and many people laid roses and carnations in the metro in memory of the dead.

Police threw up a security cordon around Moscow and stepped up spot identity checks on the streets. Based on a composite sketch of a suspect in the Friday morning attack, police detained two men for about three hours Saturday, Russian news agencies reported.The sketch, released Saturday, was based on a videotape from the subway station nearest to the blast, showing a woman believed to be the bomber and her accomplice standing on the platform before boarding the train.

An explosion tore apart a train car killing 39 people and injuring over 130 others. The blast rattled a carriage during morning rush hour as the train was travelling from Paveletskaya station to Avtozavodskaya station, southwest of the city centre, around 8:40 a.m. local time.

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