Suspected female suicide bomber Naida Asiyalova arrived in Volgograd from Makhachkala on a bus bound for Moscow, the Russian Investigative Committee said.

"As of now, investigators have questioned over 50 people among the witnesses and victims of the terrorist act," Russian Investigative Committee spokesman Vladimir Markin told Interfax.

It has been determined that Asiyalova arrived in Volgograd from Makhachkala on a Moscow-bound bus, Markin said.

"For an unknown reason she exited the bus near the Volgograd Interior Ministry Academy approximately one hour prior to carrying out the terrorist attack," the spokesman said.

It has been reported that the bus explosion in Volgograd on October 21 claimed the lives of six people and injured 36 people, four of whom are in critical condition.