The suspect in the metro train explosions in St. Petersburgsia that killed 11 people has been identified by Russian security services, it was announced on Tuesday.

"It has been established that an individual suspected of carrying out the terrorist attack is a native of our republic," Kyrgyzstan National Security Committee spokesman Rakhat Sulaimanov told TASS news agency.

According to Sulaimanov, the suspect, Akbarzhon Jalilov, also had Russian citizenship. 

Sulaimanov added that Kyrgyzstan's special services "are closely working with their Russian counterparts" in investigating the explosion.

An unidentified device went off on Monday in the metro train car when it was moving from Tekhnologichesky Institut Station to Sennaya Ploshchad Station. 

The Russian Investigative Committee termed the blast a "terrorist attack".

The Russian Emergencies Ministry said 51 people were injured.

Authorities in St. Petersburg have declared three days of mourning for the victims, the BBC reported.

President Vladimir Putin, who was in the city when the blast occurred, visited the scene on Monday evening and laid flowers at a makeshift shrine.

"Certainly, we will consider all variants, common, criminal, first of all, of a terrorist nature," RT news quoted him as saying.