At least ten people have been killed by an explosion on the St Petersburg Metro, Russian media have claimed.
The explosion, which took place between the Sennaya Ploschad and Tekhnologichesky Institut stations near the city's centre, took place at around 2:30pm local time.
President Vladimir Putin, who had been in the city on Monday, has indicated that the cause of the blast has yet to be confirmed, adding that an investigation is taking place.
“The causes of this event have not been determined yet, so it’s too early to talk about [possible causes]," he said.
"The investigation will show. Certainly, we will consider all variants, common, criminal, first of all, of a terrorist nature."
Mr Putin added that he had spoken to the head of the Russia's special services who were working to ascertain a cause.
St Petersburg's entire Metro network was shutdown following the explosion with extra security measures also being taken in Russia's capital, Moscow.
Andrey Kibitov, a spokesman for the governor of St Petersburg, has indicated that 41 ambulances were at the sites of the explosion, adding that as many as 50 people had been injured.
