At least nine people were killed and 20 were injured when an explosion tore through a train carriage in the St.Petersburg metro system on Monday, the Russian National Anti-Terrorist Committee said.
Interfax news agency quoted an unnamed source as saying the blast, which occurred when the train was between two stations, was caused by a bomb filled with shrapnel.
President Vladimir Putin, who was in the city for a meeting with Belarus's leader, said he was considering all possible causes for the blast, including terrorism and was consulting with security services.
Ambulances and fire engines descended on the concrete-and-glass Sennaya Ploshchad metro station. A helicopter hovered overhead as crowds gathered to observe rescue operations.