A suicide bomber, believed to be female, has attacked a bus travelling on a road in Volgograd, Southern Russia on Monday.
At least six people are believed to have died in the explosion, which was captured on video by a car driving behind the bus when it exploded. According to Reuters, 28 people were injured with eight in critical condition.
A 30-year-old woman from the hugely volatile area of Dagestan in the North Caucuses has been blamed for the killings, sparking fears of further insurgent attacks in the run up to the Winter Olympics in Sochi in 2014.
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Speaking to state-run Rossiya-24 television, an eye-witness said: "There was a blast - a bang - all the glass flew out of the windows," adding: "The cloud of smoke quickly dissipated and then I saw people start to fall out and run out to escape the bus," he said. "It was a horrible sight."
The attacker, named by authorities as Naida Asiyalova, is reported to be the wife of Dmitry Sokolov, a known insurgent who has been fighting on the side of the Islamic militants against Moscow's rule.