Russian security officials are hunting down three potential female suicide bombers, one of whom is believed to be in Sochi, where the Winter Olympics will begin next month.

Police leaflets seen by an Associated Press reporter at a central Sochi hotel on Tuesday contain warnings about three potential suicide bombers.

A police letter said that one of them, Ruzanna Ibragimova, a 22-year-old widow of an Islamic militant, was at large in Sochi. Russian authorities have blamed the so-called "black widows" of slain insurgents for previous suicide attacks in the country.

Security officials in Sochi were not available for comment on Tuesday. The Black Sea resort town will host the games in February amid concerns about security and potential terrorist attacks.

The southern city of Volgograd was rocked by two suicide bombings in late December, which killed 34 and injured scores more. An Islamic militant group in Dagestan posted a video on Sunday claiming responsibility for the bombings and threatened to strike the games in Sochi, about 500 kilometres west of Dagestan.

Police material distributed to the hotel staff also included pictures of two other women in veils: 26-year-old Zaira Aliyeva and 34-year-old Dzhannet Tsakhayeva. It said they had been trained "to perpetrate acts of terrorism."

'Probably among us'

It warned that the two women "are probably among us," but, unlike Ibragimova's case, did not say if they are in Sochi.

No further information was provided about the two women or their motivation. The term "black widow" refers to the belief that women who have carried out past suicide attacks in Russia did so to avenge the deaths of husbands or other male relatives.

The Olympics are to be held Feb. 7-23. Russia has mounted an intense security operation in the city, but concern persists that "soft targets" outside the Olympic venues, such as buses and tourist facilities, are vulnerable to attack.

Russian troops also have been active fighting militants in Dagestan, one of the predominantly Muslim republics in Russia's North Caucasus and the centre of an Islamic insurgency that has engulfed the region.

On Tuesday, troops shot dead the leader of a militant group, Interior Ministry spokeswoman Fatina Ubaidatova said. She said the militant, Eldar Magatov, was wanted in attacks on security forces, bombings and the extortion of businessmen.

Interior Ministry troops elsewhere in Dagestan defused an explosive device placed near a village administration building and engaged in a firefight with militants holed up in a house, the spokeswoman said.