Russia cops believe a woman from Dagestan in the restive Northern Caucuses set off a suicide bomb on a crowded bus in the city of Volgograd.  The blast which killed at least six people was captured on another motorist’s dashboard cameras as the bus rolled down the road.

“There was a blast – a bang – all the glass flew out of the windows.  The cloud of smoke quickly dissipated and then I saw people start to fall out and run out to escape the bus. It was a horrible sight,” said a witness who was driving behind the bus on the highway.

The bombing is raising fears that Islamist militant groups are planning to step up attacks on Russian targets in the run up to the 2014 Winter Olympics in the Black Sea Resort city of Sochi, next February.  Volgograd is hundreds of kilometers away from Dagestan and Chechnya, where Islamist militants seek autonomy from Moscow.

Police say the woman they suspect of detonating the bomb is the partner of a Muslim militant.