Russian security agencies have found and defused a second explosive device on the St Petersburg metro after an explosion killed at least nine people.
The device was left in a briefcase, the Interfax news agency reports.
Andrei Przhezdomsky, a spokesman for Russia's top anti-terror agency, said the improvised explosive was found at the Ploshchad Vosstaniya station.
An unidentified explosive device went off at 2:20pm on a train leaving the Technology Institute station and heading to the Sennaya Ploshchad station, Russia's National Anti-Terrorist Committee said.
The blast came as Russian President Vladimir Putin was visiting the city, his hometown. He said investigators are looking into whether the explosion was a terror attack.
News agency Interfax cited a source saying the blast was caused by a bomb filled with shrapnel.
Ambulances and fire engines descended on the concrete-and-glass Sennaya Ploshchad metro station near the centre of the former Russian imperial capital. A helicopter hovered overhead as crowds gathered.
The St. Petersburg subway immediately shut down all of its stations and the national anti-terrorism body said security measures would be tightened all key transport facilities across Russia.
