The main suspect in a blast in a St Petersburg train carriage that killed 14 people and wounded 50 is a Russian citizen originally from mainly Muslim Kyrgyzstan, authorities there said on Tuesday.

The perpetrator had radical Islamist links, Russian media cited law enforcement officials as saying, raising the possibility the attack could have been inspired by Islamic State, which has not struck a major city in Russia before.

There has been no official confirmation or claim of responsibility. The Kyrgyz GKNB security service identified the suspect as Akbarzhon Jalilov, born in the city of Osh in 1995, but provided no other details.

The explosion on Tuesday in the middle of the afternoon occurred when the train was in a tunnel deep underground, amplifying the force of the blast. The carriage door was blown off, and witnesses described seeing injured passengers with bloodied and blackened bodies.

State investigative authorities said fragments of the body of the suspect had been found among the dead, indicating that he was a suicide bomber.