A Russian citizen born in the Central Asian nation of Kyrgyzstan is considered the prime suspect in this week's deadly bombing of an underground train in central St Petersburg, authorities said.

The suspect, Akbarzhon Jalilov, 22, was killed in the explosion, a spokesperson for Russia's top investigative agency said in a statement.

Jalilov was an ethnic Uzbek born in the Kyrgyz city of Osh, Kyrgyz authorities said. He received Russian citizenship through his father, a car mechanic, when he was a teenager.

He had been living in St Petersburg and displayed a marked change in behaviour when he returned from a visit to Kyrgyzstan in February, news agency Interfax quoted a souce as saying.

Authorities believe Jalilov was radicalised by Islamic extremists there.

"Genetic traces of Jalilov were found on a bag that contained an explosive device" that was left at a station near where the bombing occurred, the Investigative Committee's spokesperson Svetlana Petrenko said.

Jalilov was earlier identified as a suspect by Kyrgyzstan's National Security Committee. Russian authorities had previously said they were seeking two Central Asian nationals - a man and a woman, each about 20 years old - after analysing surveillance camera video.

In all, 14 people were killed

The Monday incident, which struck the train en route between stations, is considered the deadliest ever terrorist attack in Russia's second-largest city. Fourteen people were killed.

Some details and names of the victims were released yesterday, among them one of the original suspects, a 20-year-old Kazakh student. The oldest victim was a 71-year-old Russian man.

About 50 wounded were still in hospital yesterday morning, Russian Health Minister Veronika Skvortsova said.

The city's governor, Georgi Poltavchenko, said that everything was being done to guarantee the safety of tourists in the city, which is a host city for football's Confederations Cup in June, and the football World Cup next year.

St Petersburg and the Russian capital, Moscow, have sizeable populations of Central Asian migrant workers who come to the country''s two largest cities for economic opportunities.

The Kremlin said foreign help might be needed in the investigation and confirmed that a suicide bomber was suspected.

The bombing occurred around 2.40pm (7.40pm in Malaysia) while the train was travelling to the central station Tekhnologichesky Institut. An undetonated bomb was found at a nearby station, Ploshchad Vosstaniya.

- dpa