The man suspected of killing 11 people in the St Petersburg metro is thought to be from Kyrgyzstan.

Kyrgyzstan's State Committee for National Security said in a statement that one suspect behind the bombing is a Kyrgyz-born Russian citizen it identified as Akbarzhon Dzhalilov.

The Kyrgyz intelligence agency said Russian authorities informed them about the man, aged between 21 and 22, but they were not aware of his specific role in the bombing. The intelligence agency said it is cooperating with Russian authorities to help the investigation.

Interfax news agency said authorities believed the 23-year-old suspect was linked to radical Islamist groups.

An unidentified explosive device went off at 2.20pm on Monday, on a train leaving the Technology Institute station and heading to the Sennaya Ploshchad station, Russia's National Anti-Terrorist Committee said.

"Everything was covered in smoke, there were a lot of firefighters," Maria Smirnova, a student on a train behind the one where a bomb went off, told the Dozhd television channel. "Firefighters shouted us to run for the exit and everyone ran. Everyone was panicking."

Kyrgyzstan's State Committee for National Security said in a statement on Tuesday it is cooperating with Russian authorities to help the investigation.

The blast came as Russian President Vladimir Putin was visiting the city, his hometown. He said investigators are looking into whether the explosion was a terror attack.

Interfax cited a source saying the blast was caused by a bomb filled with shrapnel.

A second bomb was found and defused by police.

Kyrgyzstan is a former Soviet republic which gained independence in 1991.