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 at least five people and injured more than 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.
Authorities in the Volgograd region announced Monday that a three-day period of mourning for victims of the explosion will begin Tuesday.