Russian President Vladimir Putin has blamed Chechen separatists for a bomb attack on the Moscow underground railway that killed at least 39 people.
Moscow police said a suicide bomber probably triggered the blast
Mr Putin said he did not need any indirect confirmation - he was certain that rebel leader Aslan Maskhadov and his forces were behind the explosion.
But Chechen leaders condemned the blast, that also injured more than 100.
Russian police are studying CCTV film of two women and a man who they say may have been involved in the bomb attack.
Moscow has been hit by a series of bombings in recent years - almost all of them blamed on Chechen rebels.
Friday's blast was the bloodiest such attack in Moscow since Russia launched its second war in Chechnya in 1999, and comes five weeks before a presidential election in which Vladimir Putin is seeking a second term.
The explosion at about 0840 (0540 GMT) ripped through the second carriage of a train which had just left Avtozavodskaya Station.
There was pandemonium as passengers fled the scene after the blast, which was estimated to be equivalent to about 5kg (11lbs) of TNT.
The Russian leader said he refused to negotiate with "terrorists" and pledged Russia would destroy them.
US President George W Bush said he telephoned Mr Putin and condemned "in the strongest terms the terrorist attack on the Moscow subway".
Moscow Deputy Prosecutor Vladimir Yudin said evidence so far suggested "that the explosion in the metro car was committed by a suicide bomber".
The BBC's Angus Roxburgh in Moscow says closed-circuit television pictures show two women who may have been involved.
But, he says, police have also issued a photo fit picture of a male suspect and some officials have cast doubt on the suicide theory.
Police issued a photofit of a male suspect
They say a device may have been left in a bag on the train and that the debris did not contain the usual traces left by a suicide bomb.
Windows shattered and the carriage was turned into a hulk of twisted metal, with bodies still in their seats. Bodies also lay on the tracks
Scores of dazed commuters, many with faces bloodied by injuries and blackened with smoke, poured into the city streets to escape the flames.
Injured passengers were guided to safety through the tunnel by emergency services while fire officials attempted to put out a large fire caused by the explosion.
Around 120 people were reported to have injured - many of them suffering from broken bones, smoke inhalation and burns.
More than 50 ambulances arrived at the scene and helicopters hovered near Paveletskaya Station - where the train was headed - warning travellers the station was closed.
One woman who works in a shop near the site described horrific scenes as emergency workers struggled to cope with the scores of victims.
MOSCOW'S DEADLIEST ATTACKS
Dec 2003 - female suicide bomber kills five near Red Square
July 2003 - aborted suicide attack kills bomb disposal expert
July 2003 - suicide bombers kill 14 at Moscow rock concert
Oct 2002 - suicide attackers seize Moscow theatre, 130 hostages die in rescue
Aug 2000 - bomb in underpass kills 11
Sept 1999 - two blasts in blocks of flats kill more than 200
"We saw them carrying bodies and injured covered in blood," she told French news agency AFP.
"A man came into the shop, he was shaking uncontrollably and covered in blood.
"He told us that he saw arms, legs scattered around the carriage. He said it was bloody carnage."
Some nine million people use the metro system every day and the blast is likely to spread fear across the city.
Chechen militants have previously targeted the Russian capital with suicide missions and the city has been on alert for attacks as the country prepares for next month's election.