From BBC News:
An attack on a train station in Russia’s southern city of Volgograd has killed 15 people, officials say.
A female suicide bomber was thought to be responsible for the blast, Russia’s top investigative agency 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.
Russian President Vladimir Putin has ordered law enforcement agencies to take “all necessary security measures” in the bomb’s aftermath, said a Kremlin spokesman.
Mr Putin has ordered the most gravely injured victims to be flown to Moscow for treatment.
Security would be stepped up at train stations and airports, said a federal police spokesman.
