The death toll from Monday's St Petersburg underground metro train blast has increased from 10 to 11.
Another 45 people were injured in the explosion.
Russian PM Dmitry Medvedev has called the explosion a "terrorist attack."
Russian media reported that the blast suspect was a 23 year old from Central Asia having links to radical Islam.
No terrorist group has claimed responsibility.
The St Petersburg metro blasts
Train operator's decision to keep driving helped save lives
The blast occurred around 14:30 hrs local time after the train left Sennaya Ploshchad metro station for Tekhnologichesky Institut.
Initially, there were reports of two explosions, but Russian investigators clarified there was only one.
Following the blast, the train operator continued driving the train till the Tekhnologichesky Institut station.
Authorities said this decision helped save lives as it quickened rescue efforts.
Tributes pour in
Putin pays tribute to victims, three days of mourning announced
Hundreds of people paid tribute to the victims of the St Petersburg metro blast.
City authorities have declared three days of mourning.
Russian President Vladimir Putin, who was in St Petersburg, laid flowers at a makeshift shrine near the blast site.
The head of Russia's defence committee, Senator Viktor Ozerov, said anti-terror mechanisms appeared to have failed and has called for an investigation.
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World leaders, including PM Modi, condemn blast
Indian PM Narendra Modi said he was "deeply saddened" by news of the blast while US President Donald Trump called it "a terrible thing." German Chancellor Angela Merkel said the attack was a "barbaric act." The EU said Europe's thoughts were with the Russian people.
Expert: ISIS-inspired groups or Chechen nationalists may be responsible
An investigation into the blast is ongoing.
He said Russia's FSB intelligence service, the successor to the Soviet-era KGB, will "focus on two possible suspects, neither yet confirmed. First, an IS-inspired group enraged by recent Russian airstrikes in Syria. And second, Chechen nationalists (or even a combination of both)."
Second, more powerful explosive device found at another station
An explosive device was found laid up against a wall at the Ploshchad Vosstaniya metro station. Reports said it contained 1kg of TNT, more than what was used in the original blast. The device was safely defused.
Terrorists have targeted Russia's transport infrastructure previously as well
In 2013, 31 people were killed in two simultaneous blasts by suicide bombers in Volgograd's central station and a trolleybus.
In 2011, a bombing at Moscow's Domodedovo airport killed 35 people.
In 2010, an attack by two female suicide bombers in the Moscow metro killed 38 people.
In 2019, an explosion triggered by Islamist militants killed 27 people in a Moscow-St Petersburg express train.