A suspected suicide bomb aboard a Moscow underground train in the early rush-hour this morning killed at least 39 passengers and injured more than 100.
Police attributed the blast, which blew out windows and ignited a fire, to a suicide bomber, and President Mr Vladimir Putin accused Chechen rebel leader Aslan Maskhadov of being behind the explosion.
"We do not need any indirect confirmation. We know for certain that Maskhadov and his bandits are linked to this terrorism," he told reporters.
But a spokesman for the fugitive separatist leader denied Maskhadov's involvement in what he described as "a bloody provocation" and condemned the explosion.
The blast occurred at 8.30 am (5.30 Irish time) in the second carriage as the train bringing commuters into the city sped through a tunnel towards Moscow's busy Paveletskaya station.
"As of now, there are 39 dead and 129 people being treated for injuries in hospital," Deputy Interior Minister Mr Alexander Chekalin told reporters.
Moscow deputy mayor Mr Valery Shantsev said the blast had been caused by five kgs (nearly 11 lbs) of explosives.
One woman said survivors walked about two km (a mile) along the tracks to safety after clambering from the train that had been crammed with morning commuters travelling into the capital.
"I heard a terrible explosion and almost fell over," said 18-year-old student Alexander Maksimov, his face pale and hands shaking. "My first thought was to run outside to the fresh air, but from the shock I could hardly move."
Suicide bomb attacks in Moscow and elsewhere in Russia have been the trademark of Chechen separatists fighting Russian forces for independence in their Muslim Caucasus homeland.
If confirmed, it would be the worst such attack by Chechen suicide bombers in Moscow since July 2003 when two women blew themselves up at an open-air music festival at the Tushino airfield, killing 14 other people.
Mr Putin, widely expected to win re-election easily in a March 14th poll, used the Chechnya issue to boost his popularity when he was first elected to the Kremlin in 2000.
Talking tough following apartment block bombings in Moscow and two other Russian cities in September 1999 helped him get elected a few months later.
More than 200 people were killed in those attacks for which two Chechen-trained fighters were recently jailed.
Though his high popularity never appears to be dented by such attacks, he said on Friday that he felt such incidents could be used as political ammunition against him in next month's poll, Itar-Tass news agency said.
A statement, signed by Akhmed Zakayev, on the rebel website said: "The president and government of the (separatist) Chechen Republic of Ichkeria hereby declare that they are in no way connected to this bloody provocation and unequivocally condemn it."
News of the explosion rattled Moscow's financial markets helping send the dollar-denominated RTS index down nearly two percent at the opening. The rouble was also slightly weaker.
Pictures of the inside of the devastated carriage showed bodies lying among twisted metal and shredded seats.