Russian officials say Monday's explosion on a passenger bus in the southwest Russian city of Volgograd was the work of a female suicide bomber.
The blast killed six people along with the bomber, and injured about 30.
Russia's Investigative Committee identified the suicide bomber as Naida Asiyalova. Committee spokesman Vladimir Markin said she was a 30-year-old resident of Dagestan, one of the republics in Russia's predominantly Muslim North Caucasus region.
In recent years Dagestan has become the epicenter of the ongoing Islamist insurgency in the North Caucasus.
No one has claimed responsibility for the bus blast.
In early July, the leader of the Islamist insurgency in the North Caucasus, Doku Umarov, declared an end to a moratorium on attacks on Russian civilian targets he had announced the previous year.
He also called on insurgents to target the 2014 Winter Olympics set to take place next February in Sochi, not far from the North Caucasus.
President Vladimir Putin's press secretary, Dmitry Peskov, said Monday the Russian leader had conveyed his condolences to victims of the Volgograd bus bombing.
Authorities in the Volgograd region announced that a three-day period of mourning for victims of the explosion will begin Tuesday.