Russian officials have made no public accusations, but the attack by a female bomber bore hallmarks of actions by Chechen rebels seeking independence for their Caucasus mountain region.

It came a week after 90 people were killed in two simultaneous air crashes officials blame on suicide bombers and followed a sensitive Chechen elections on Sunday.

"We cannot rule out a Chechen trail," Itar-Tass news agency quoted an Interior Ministry source as saying after the attack toward the end of the evening rush hour near a metro station and crowded shopping center.

Officials said 14 people were still in a serious condition in hospital with wounds from the bomb which had been packed with bolts and other shrapnel and which caused two parked cars to explode into flames.

A militant Islamist group claimed responsibility. In a web site statement, the Islambouli Brigade vowed further attacks on "infidel" Russia in support of Muslim Chechen rebels.

Russian officials treated with skepticism a similar claim of responsibility from the little-known Islambouli Brigade for the August 24 air crashes that killed 90 people.

They were likely to be equally wary of the group's claim over the Moscow bombing, seeking perpetrators at home rather than beyond Russian frontiers.

Two women from Chechnya, listed among the passengers of the crashed planes, are viewed as prime suspects. It took several days for investigators to establish sabotage in the crashes.

The new bomb attack fueled nervousness among Muscovites, already on their guard after newspaper reports that two other Chechen would-be female suicide bombers were still on the loose after the plane crashes.