- NEW: Russia authorities say preliminary information points to a female suicide bomber
- It is the second bombing in the Russian city of Volgograd in two months
- In October, Russian reports say, a female Islamist suicide bomber blew up a bus in Volgograd
- The Winter Olympics in Sochi start in less than six weeks
Moscow (CNN) -- An explosion at a train station in Volgograd, Russia, killed at least 18 people on Sunday, Russian media reported.
The RIA Novosti news agency also said dozens were injured, citing police. The ITAR-TASS news agency reported a lower death toll of 13.
Russia's National Anti-Terror Committee told CNN that preliminary information suggests the blast was caused by a female suicide bomber.
It is the second bombing in the southern Russian city in two months and comes less than six weeks ahead of the Winter Olympics in Sochi, located less than 1,000 kilometers (620 miles) from Volgograd.
No one has claimed responsibility for the attack.
In October, a bomber blew up a passenger bus, killing six people and wounding more than 30 others. Russian media reported that a female Islamist suicide bomber from the Russian region of Dagestan was responsible for the attack.
The restive region of Chechnya is also located in this southern portion of Russia.
CNN's Diana Magnay contributed to this report
