Russian authorities say they are almost certain that one of the suicide bombers who attacked the Moscow Metro on Monday was a 17-year-old girl from Dagestan.
The girl, Dzhennet Abdurakhmanova, is believed to be the widow of a senior Caucasus militant killed by Russian security forces late last year.
Dagestan, like nearby Chechnya, is struggling to quell militant violence.
The morning rush-hour bombings killed 40 people and injured more than 80, most of whom are still in hospital.
"One of the female suicide bombers, who blew herself up at the Park Kultury metro station, was Dzhennet Abdurakhmanova," said a statement from Russia's National Anti-Terror Committee (NAK) carried by the RIA Novosti and Interfax news agencies.
"She was born in 1992 and lived in the Khasavyurtsky region of Dagestan."
A police spokesman said earlier that the suspect had been married to a leading Islamist militant, Umalat Magomedov, who was killed by Russian security forces at the end of last year.
A photograph of her published in a leading Russian newspaper, Kommersant, bears a strong resemblance to a picture of the remains of one of the suicide bombers, the BBC's Richard Galpin reports from Moscow.
The identity of the second bomber has not been confirmed, but Kommersant said she may have been the widow of another Chechen militant killed last year.
Abdurakhmanova is believed to have travelled to Moscow by bus with the other female suicide bomber from the Dagestan town of Kizlyar, near the Chechen border.
The death toll from their twin bombings rose to 40 on Friday after one man died from his wounds in hospital, officials said.
On Wednesday 12 people, nine of them police officers, were killed in two suicide bombings in Kizlyar.
In Moscow, the news that the attacks were carried out by women had fuelled speculation that they were so-called "black widows" - women married or related to militants killed by Russian forces in areas such as Dagestan, Ingushetia and Chechnya.
Black widows have been involved in several major attacks in the North Caucasus and in Moscow.
Rebel's video warning
Unnamed Federal Security Service (FSB) officials say Magomedov was an associate of Doku Umarov, the Chechen rebel leader who claims he ordered Monday's metro attacks.
In a video message posted on a rebel website, Mr Umarov warned Russians to prepare for more attacks.
On Thursday, Russian President Dmitry Medvedev flew to Dagestan's capital Makhachkala to hold emergency talks with the leaders of Russia's troubled North Caucasus republics.
"We must deal sharp dagger blows to the terrorists; destroy them and their lairs," Mr Medvedev said.
"The list of measures to fight terrorism must be widened. They must not only be effective but tough, severe and preventative. We need to punish."
The attacks came almost a year after Mr Medvedev declared an end to Russia's "counter-terrorism operations" in Chechnya, in a bid to "further normalise the situation" after 15 years of conflict that claimed more than 100,000 lives and left it in ruins.
Despite this, the mainly Muslim republic continues to be plagued by violence, and over the past two years Islamist militants have stepped up attacks in neighbouring Ingushetia and Dagestan.
Mr Umarov said the attacks were an act of revenge for the killings of Chechen and Ingush civilians by the Russian security forces near the town of Arshty on 11 February.
The rebel, who styles himself as the Emir of the Caucasus Emirate, said attacks on Russian soil would continue. - BBC