Russian officials say they believe a female suicide bomber caused an explosion that killed at least 16 people and wounded dozens Sunday at the entrance to a train station in Volgograd. The latest attack in southern Russia occurred about 650 km northeast of Sochi, which will host the Winter Olympics in February.
Russia's federal investigative committee says the bomber walked into a busy train station in Volgograd and detonated explosives just in front of metal detectors.
Vladimir Markin, who heads Russia's Investigative Committee, said that this explosion was the equivalent of 10 kg of TNT.
He said there would have been many more victims if the so-called guarding system at the train station hadn't worked. He pointed out that security did not allow the suicide bomber to get through the metal detector into the waiting hall where at the time there were lots of people because three trains were late.
This is the second recent deadly bombing in the city of around one million. In October, a female suicide bomber blew herself up at a bus stop, killing six others.
Volgograd is around 650 km northeast of Sochi, the site for the upcoming Winter Olympics, a pet project of Russian President Vladimir Putin.
In an online video, Chechen militant leader Doku Umarov has called on rebels to use maximum force to prevent Putin from staging the Olympics. Putin has maintained that the games will be safe and that the Kremlin has taken every necessary precaution.
Sochi is situated near the volatile North Caucasus region, on Russia's southern flank. The region has seen violence for more than a decade as rebels try to establish an Islamist state. There are near-daily attacks on police and officials in the region. Critics blame the violence there on the Kremlin's crackdown on dissent.
Sunday's train-station attack is believed to be the deadliest in three years. In 2011, 37 people were killed when Islamist insurgents bombed a Moscow airport.
On Friday, three people died in another attack some 270 km east of Volgograd, in the city of Pyatigorsk.