Security fears have been heightened ahead of the Sochi Winter Olympics following news of a second bomb attack that has rocked Russia.
At least 10 people are thought to have died in the blast, which tore through a trolleybus in the city of Volgograd.
It comes just a day after 17 were killed in a suicide attack at the city's central station.
According to BBC News, Moscow is concerned that militant terrorist groups are trying to destabilise preparations ahead of the Games in Sochi, which is 700km north-east of the volatile Chechen region.
As a result, security at airports and train stations has been tightened amid the growing threat of violence.
The Games get underway in February.
