The Latvian Ministry of Foreign Affairs asked any Latvians in St Petersburg to let their loved ones know they were safe.
Phone numbers and contact details were provided for anyone in need of consular assistance. Latvia maintains a consul in the city.
"If in need of consular assistance, please call the Ministry of Foreign Affairs at the round-the-clock emergency phone +371 26337711 or apply to the Consulate General of Latvia in St. Petersburg," the ministry said.
There were no immediate indications that Latvians might be among the dead or injured.
Foreign Minister Edgars Rinkevics was in doubt that the explosions were the result of a "criminal act" and called for the perpetrators to be brought to justice.
Terrible news about blasts in #SaintPetersburg metro, perpetrators of this crime must be punished, deep condolences to relatives of victims— Edgars Rinkēvičs (@edgarsrinkevics) April 3, 2017
President Raimonds Vejonis followed suit:
Terrible blasts in #SaintPetersburg metro, condemn attacks against innocent civilians, deep condolences to the relatives of victims.— Valsts prezidents (@Rigas_pils) April 3, 2017