Russian President Vladimir Putin has linked yesterday's attack on a subway train in Moscow with unrest in Chechnya and next month's Russian Presidential elections.
Yesterday's rush-hour bombing killed at least 39 passengers, and police said 113 people were still in hospital, among them a nine-year-old boy.
Officials gave different explanations for the blast, which shattered the second carriage of a packed train as it was speeding between two central Moscow stations.
Some suggested the blast was caused by a package left on board. Deputy Moscow prosecutor Vladimir Yudin said the most likely scenario was a suicide bombing - like a series of other attacks which have struck the capital in recent months.
Putin, addressing reporters alongside the president of ex-Soviet Azerbaijan, claimed the fugitive Chechen separatist leader Aslan Maskhadov had masterminded the attack.
"We do not need any indirect confirmation. We know for certain that Maskhadov and his bandits are linked to this terrorism," he said.
"I do not rule out that this could be used both in debates taking place in the Russian presidential election and as a lever to put pressure on the current head of state."
A spokesman for the fugitive Chechen leader said neither Maskhadov nor his separatist government were "connected to this bloody provocation and (they) unequivocally condemn it".
Putin, his poll ratings over 70 percent, has never been hurt by attacks like Friday's train blast and used the fight against separatists to his advantage in first winning election in 2000.
He is unlikely to have any trouble defeating up to six rivals in the March 14 vote. The list of candidates who have met stiff requirements to take part is to be announced by Sunday