Security sources in the southern Russian region of Dagestan say a female suicide bomber has injured at least 11 police officers and civilians.
Vyacheslav Gasanov, Dagestan's police spokesman, said the bomber blew herself up on Saturday on the central square in the provincial capital, Makhachkala.
Since 2000, at least two dozen female suicide bombers, most of them from the Caucasus, have carried out attacks in Russian cities and aboard trains and planes.
All were linked to theinsurgency that spread throughout Dagestan and the predominantly Muslim Caucasus region after two separatist wars in neighbouring Chechnya.
The bombers are often called "black widows" in Russia because many of them are the wives, or other relatives, of fighters killed by security forces.