The death toll from the bomb blast in St. Petersburg has risen to 14, Russian Health Minister Veronika Skvortsova said on Tuesday.‍

‍‍‍A total of 51 people were injured in the metro explosion and are staying in hospitals, St. Petersburg Chief Administration of Ministry of Emergency Situations said in a statement.

"Based on the data of the health committee of St. Petersburg, we are publishing the list of people injured in the emergency situation in the St. Petersburg metro, who are now remaining in the hospitals of the city. Please note that this list is relevant as of 03.00 a.m. [00.00 GMT], April 4, and will be updated when [newer] information becomes available," the statement reads.

Interfax news agency quoted an unnamed source as saying the blast, which occurred when the train was between two stations, was caused by a bomb filled with shrapnel.

Kyrgyzstan's security service on Tuesday named the suspect in the deadly blast as Akbarjon Jalilov, a Kyrgyz-born Russian citizen. The security service pledged to work with Russia on the investigation into the incident. A spokesman for the GKNB security service identified the suspect as being born in the city of Osh in 1995. He provided no other details.

CGTN spoke to security expert Sajjan Gohel, who said he believes the blast was a revenge attack by terrorists, angered by Russia and other Western nations. 

Russia's state investigative committee later confirmed the statement from Kyrgyzstan's security services.

The committee said its investigation had identified Jalilov as the suspect, whose genetic traces were also found on a bag containing an explosive device.

"From the genetic evidence and the surveillance cameras there is reason to believe that the person behind the terrorist act in the train carriage was the same one who left a bag with an explosive device at the Ploshchad Vosstaniya station," the committee added.

President Vladimir Putin, who was in the city for a meeting with Belarus’s leader Alexander Lukashenko, said he was considering all possible causes for the blast, including terrorism, and was consulting with security services.

Putin also paid tribute to the victims by laying flowers at the entrance of the subway station where the explosion took place, and expressed his condolences with the families of those killed and injured. 

St. Petersburg emergency services at first said that there had been two explosions. But a source in the emergency services later said that there had been only one but that the explosion had occurred in a tunnel between stations.

Video showed injured people lying bleeding on a platform, some being treated by emergency services and fellow passengers. Others ran away from the platform amid clouds of smoke, some screaming or holding their hands to their faces.

A huge hole was blown open in the side of a carriage with metal wreckage strewn across the platform. Passengers were seen hammering at the windows of one closed carriage. Russian TV said many had suffered lacerations from glass shards and metal.

Russia has been the target of attacks by separatist Islamist Chechen militants in past years. ISIL, which has drawn recruits from the ranks of Chechen rebels, has also threatened attacks across Russia in retaliation for Russian military intervention in Syria.

The Russian air force and special forces have been supporting President Bashar al-Assad in fighting rebel groups and ISIL fighters now being driven out of their Syrian strongholds.

United Nations Secretary-General António Guterres condemned Monday's explosion and underlined the need to bring those responsible to justice.

According to a statement issued by Guterres’s spokesperson, the UN chief expressed his deepest condolences to the families of the victims and to the government as well as to the people of Russia.

He also underscored that those responsible for the “appalling act” must be held accountable.

Authorities closed all St. Petersburg metro stations in the aftermath of the attack, but the network has now reopened. The Moscow metro said it was taking unspecified additional security measures in case of a further attack.

Russia has been on particular alert against Chechen rebels returning from Syria and wary of any attempts to resume attacks that dogged the country several years ago.

At least 38 people were killed in 2010 when two female suicide bombers detonated bombs on packed Moscow metro trains.

Over 330 people, half of them children, were killed in 2004 when police stormed a school in southern Russia after a hostage taking incident by Islamist militants. In 2002, 120 hostages were killed when police stormed a Moscow theater to end another hostage-taking incident.

Putin, as prime minister, launched a 1999 campaign to crush a separatist government in the Muslim southern region of Chechnya, and as president has continued a hard line in suppressing rebellion.