Russia's health minister has confirmed ten people have been killed and at least 50 injured, in an explosion on the Metro system in the city of St Petersburg.

A second device was also found and has been made safe.

It's understood the blast happened between two stations.

Russian President Vladimir Putin isn't ruling out terrorism:

Sky News Russia correspondent John Sparks says the bomb went off in a tunnel between Sennaya Ploshchad and Tekhnologichesky Institut stations.

.@WarfareWW VIDEO: Aftermath of the explosion in St. Petersburg metro #Russia - @RobPulseNews pic.twitter.com/vnYt6B3JQW

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