The first threat came from a drunk man who on Tuesday told a police officer at metro station Medvedkovo that there would be an explosion in the metro Wednesday, police said. The man did not say at what station the attack would take place. Police charged him with public drunkenness and took him to a hospital.
A second warning of a metro bomb attack came from an anonymous caller.
Police have dispatched canine bomb-sniffing units to central and transfer metro stations and assigned military officers to patrol stations.