At least 11 people were killed in an explosion in Saint Petersburg metro on Monday, with dozens injured.
The blast tore apart a train carriage which was travelling between two stations around 2.40 pm.
A second explosive device was found at a nearby station and defused by authorities. No groups have claimed responsibility for the explosion.
President Vladimir Putin said the cause of the explosion was not clear yet. “We will look at all possible causes, terrorism as well as common crime,” Putin said.
Russia’s Investigative Committee said while the investigation into the event was based on an assumption of terrorism, it was also considering other possibilities.
According to state media, the bomb contained a kilogram of TNT and was hidden in a fire extinguisher. Law enforcement agencies also confirmed that the bomb was filled with shrapnel.
All St Petersburg metro stations have been closed.