Authorities reported at least 50 people had been injured and 14 people were killed after an explosion between two underground metro stations in Russia's second-largest city on Monday.
Prime Minister Dmitry Medvedev described the blast as a "terrorist attack." Although, an anti-terror investigation has been initiated, other potential causes are also being investigated.
The suspected suicide bomber is believed to have been a Kyrgyzstan native who had later obtained Russian citizenship, the central Asian country's security service said on Tuesday.
"The Kremlin has experienced two unexpected and jarring incidents in just over a week, and this could lead to action against dissent that is stronger than it would otherwise be," Eurasia Group analysts said in a note.
"Such action would add to U.S. and European governments' criticisms of the arrests that followed the 26 March protests."