Terrorism threatens to cast shadow over Sochi Winter Olympics

Vladimir Putin's daring bid to host the Winter Olympics in the politically dicey Caucasus Mountains was his way of showing to the world that he had created a stylish, fun-loving country, a Russia that had defeated violent separatism once and for all.

It was a gutsy gamble - and the remaining separatists vowed to do whatever they could to disrupt the pageant. The potential costs of failure were driven home on Monday when an apparent suicide bomber shredded a crowded trolleybus in the city of Volgograd. That came on the heels of a bomb attack on the city's railroad station the day before. The two explosions killed 31 people and injured dozens more.

Security at the site of the Olympics is watertight, so Islamist extremists have vowed to bring violence to the Russian heartland. Volgograd, 650 kilometres from Sochi, and a city storied in Russian history, offers a tempting target.

Putin demanded a tightening of security on Monday amid fears that foreign guests in particular could be frightened away from the Winter Games, scheduled for February 7-23. The two bomb blasts effectively blunt his recent charm offensive, seemingly aimed at the West with the Olympics in mind, that saw the release of the oil tycoon Mikhail Khodorkovsky, two of the Pussy Riot members and the crew of the Greenpeace ship Arctic Sunrise, held on criminal charges since late summer.

Although no groups claimed responsibility for the Volgograd attacks, officials said they believe they were related - and linked to an extremist group in Dagestan.

Russia has been engaged in an enduring and violent struggle with extremists since it defeated a separatist movement in Chechnya in the 1990s. After the war, a growing number of separatists turned radical, evolving into Islamist extremists who have launched sporadic terrorist attacks from Moscow to the hinterlands. They have also carried out a low-grade battle with authorities, now centred in the southern region of Dagestan, inflicting casualties among Russian forces more numerous than the US military suffers in Afghanistan.