Footage of the suicide bombing of Russia's Volgograd train station

An explosion at a train station in the southern Russian city of Volgograd has killed at least 13 people, reports say.

A female suicide bomber was responsible for the blast, which injured 50 people, Russia's anti-terrorism committee said.

A suspected female suicide bomber killed at least six people when she attacked a bus in the city in October.

Moscow is concerned militant groups could be ramping up violence in the run up to the the 2014 winter Olympic Games in the city of Sochi in six weeks.

An Islamist insurgency in the North Caucasus region has led to many attacks there in recent years. Insurgents have also attacked big Russian towns.

Volgograd lies about 900km (560 miles) south of Moscow, 650km north of the North Caucasus and 700km north-east of Sochi.

No group has yet claimed responsibility for Sunday's explosion.

It rocked Volgograd station at around 12:45 (08:45 GMT). Footage from the scene showed bodies laid out beside ambulances parked in the station forecourt, and debris strewn on the station steps.

In July, Chechen insurgent leader Doku Umarov posted an online video urging militants to use "maximum force" to prevent the Games from going ahead.