At least seven people died and dozens of others were injured on Monday when a female suicide attacker blew herself up on a bus in the southern Russian city of Volgograd, authorities said.
"According to preliminary reports, Dagestani native Naida Asiyalova, 30, blasted herself", the Russian Investigation Committee spokesman Vladimir Markin told reporters.
"This woman got on the bus at a bus stop and the explosion went off almost immediately after this," Markin said, adding that it had been confirmed by a survivor of the blast.
Six passengers, and the suicide bomber were killed. Thirty- three people, including one child, have sought medical assistance, he said, adding that eight of them injured people are in " extremely grave condition."
The terror attack reportedly occurred at around 2 p.m. (1000 GMT). Officials have filed charges of "terrorist attack, murder, and use of illegal weapons," the Investigative Committee said.
Local media said Asiyalova is the wife of a Dagestani gang Dmitry Sokolov.
"They studied together at a Moscow higher educational institution, where the young woman recruited Sokolov ... He went to Dagestan and joined the gunmen," the Itar-Tass news agency quoted an unnamed source from local law enforcement agencies as saying.
Investigators have talked to witnesses and survivors of the attack and are also studying the recordings of video surveillance cameras.
The bomb size and type will be identified in forensic tests ordered by the investigators.
Kremlin spokesman Dmitry Peskov told reporters that special services are providing updated reports to President Vladimir Putin, who has conveyed deep condolences to the families and relatives of the victims killed in the terror attack.
A three-day mourning starting on Tuesday in the Volgograd region has been declared.
The regional government's press service said in a statement that the families of the victims killed in the explosion will each get one million rubles (31,000 U.S. dollars) in compensation payments from the regional budget.
"Payouts to seriously injured victims will amount to 400,000 rubles (12,500 dollars) and to other injured victims 100,000 rubles (3,125 dollars)," the statement said.