The death toll in the Minsk metro blast rose to 12 as one of the victims died in hospital early on Tuesday, the country's security service said in a statement, RIA Novosti reported.
The Belarusian KGB also said the most likely perpetrator of the attack has already been identified.
The blast was officially classed as terrorism as the criminal case was launched.
More than 120 people were injured when a bomb exploded as a train stood at the Oktyabrskaya metro station at 5.55 pm (14:55 GMT) on Monday. The bomb was planted under a bench at the metro's only interchange station, the city's busiest.