Russian investigators believe one of the suicide bombers who attacked Moscow's underground train network this week was a teenage girl.
She is said to have been the 17-year-old widow of a militant from the North Causasus region, who was killed by Russian security forces late last year.
The girl was believed to be from Dagestan, which, like nearby Chechnya, is struggling to quell militant violence.
Two women blew themselves up in the attacks on Monday, which killed 40 people.
The identity of the second bomber has not been confirmed, but Russian newspaper Kommersant said she may have been the widow of another Chechen militant killed last year.
