At least 18 people were killed and scores were wounded Sunday by a female suicide bomber at a railway station in southern Russia, officials said, heightening concern about attacks ahead of February's Olympics in the Black Sea resort of Sochi.
No one immediately claimed responsibility for Sunday's attack in Volgograd. It came several months after Chechen rebel leader Doku Umarov called for new attacks against civilian targets in Russia, including the Sochi Games.
Volgograd is 550 miles south of Moscow and about 600 miles northeast of Sochi, a Black Sea resort flanked by the North Caucasus Mountains.
Suicide bombings and other attacks linked to Islamic rebels roaming the North Caucasus have rocked Russia for years. The government has deployed tens of thousands of soldiers, police and other security personnel to protect the Olympics, President Vladimir Putin's pet project, and organizers have pledged to make the Sochi Games the "safest Olympics in history."
Still, sports economist and Smith College professor Andrew Zimbalist told Al Jazeera on Friday that the fear of attacks would deter some tourists from attending the Games, which are expected to cost upward of $60 billion – the most in Olympic history, and well over 30 percent more than the 2008 Beijing Olympics.