At least 10 people were killed and 50 injured when an explosion tore through a train carriage in the St. Petersburg underground system on Monday, Russian authorities said.
Interfax news agency quoted an unnamed source as saying the blast was caused by a bomb filled with shrapnel.
President Vladimir Putin, who was himself in St. Petersburg for a meeting with Belarussian leader Alexander Lukashenko, said he was considering all possible causes for the blast, including terrorism. He was consulting with security services