At least 13 people have been killed and scores wounded by a suicide bomber at a railway station in southern Russia, officials said.
The National Anti-Terrorist Committee said the explosion on Sunday at the central railway station in the city of Volgograd was set off by a suicide bomber, heightening concerns about terrorism ahead of February's Olympics in the Black Sea resort of Sochi.
Vladimir Markin, a spokesman for the nation's top investigative agency, the Investigative Committee, said at least 13 people died in the blast.
Russia's Health Ministry said about 50 people were injured.
No one immediately claimed responsibility for Sunday's attack, but it came months after Chechen rebel leader Doku Umarov called for attacks against civilian targets in Russia, including the Sochi Games.
Suicide bombings and other attacks linked to Islamic rebels have rocked Russia for years.
In October, a female suicide bomber blew herself up on a city bus in Volgograd, killing six people and injuring about 30.
Officials said the attacker came from the province of Dagestan, which has become the centre of an Islamist insurgency that has spread across the region after two separatist wars in Chechnya.
Russian state television reported that Sunday's explosion occurred at the security gate at the station's entrance.
Footage from a security camera facing the station that was broadcast by Rossiya 24 television showed the moment of explosion: a bright orange flash inside the station behind the main gate followed by plumes of smoke.
The television showed a line-up of ambulances outside the station and motionless bodies placed on the pavement.
The blast closely followed another attack on Friday in Pyatigorsk in the North Caucasus mountains, when a car rigged with explosives blew up on a street in the city, the centre of a federal administrative district intended to stabilise the North Caucasus region.
