MOSCOW -- Russian President Vladimir Putin said Thursday that the explosion at a St. Petersburg supermarket on Wednesday was an act of terrorism.

"You know that yesterday a terrorist act was committed in St. Petersburg, and some time ago the Federal Security Service (FSB) prevented another terrorist attack attempt," Putin told an award ceremony in the Kremlin for Russian servicemen who served in Syria, according to a Kremlin transcript.

An explosive device placed in a locker went off at a supermarket in a shopping center in the northern part of St. Petersburg at about 18:45 (1545 GMT) on Wednesday, injuring 13 people, according to latest reports.

So far, no one has claimed responsibility for the blast.

Putin praised Russia's contribution to the latest defeat of Islamic States (IS) militant group in Syria.

The president said he had ordered security forces to take resolute measures on terrorists of Russian origin who have returned home.

Putin said he has given instructions to the FSB director to act within the framework of law, adding that actions would be taken to take out the terrorists on the spot if there is a threat to Russian servicemen and officers.