Italian Premier Paolo Gentiloni on Monday took to social media to voice his "dismay" at the attack.
"Dismay at the metro attack. Solidarity to the victims' families. Italy close to Russian government and people," Gentiloni tweeted.
Consul General Leonardo Bencini said that the Italian consulate in St Petersburg is contacting Italians in the Russian city to verify their safety.
"The identity of the victims is not yet known; the consulate moved immediately and we set up a crisis unit to follow the situation," Bencini added.
The consul said there were around 600 Italians registered as living in St Petersburg, but that the actual number of co-nationals present is much higher as many Italians are visiting the city at the moment.
Bencini also affirmed that the consulate had activated a round-the-clock emergency number to supply assistance to Italians in the city.
Russian President Vladimir Putin stated that though the cause of the incident is not yet clear, it is being treated as a terrorist attack.
