Information thus far indicates the cause was an "unidentified explosive device", Andrei Przhezdomsky, spokesman for the National Anti-terrorist Committee, said to Rossiya-24 TV.
Commuters posted pictures and video of the aftermath of the explosion on social media.
"The causes are not yet clear, and so it's still early to talk about that, the investigation will show. We will look at all possible causes, terrorism as well as common crime", Putin said.
Gonzaga, N Carolina title game features beastly bigs
Collins and Karnowksi then accounted for the next 7 points, including a 3-pointer by Collins and a thundering dunk by Karnowski. They'll certainly have their hands full against Gonzaga however, as the Zags have extremely talented big men of their own.
The St. Petersburg prosecutor's office declared the incident a terrorist attack.
No group or individual has claimed responsibility for attack and Russian Federation hasn't blamed terrorism yet.
Foreign ministers of Britain Boris Johnson and President of Turkey Recep Tayyip Erdoğan reacted to the attack in St. Petersburg. If the prosecution spoke of a single explosion, a source in the security forces quoted by Ria Novosti referred to "two explosions of machines that were operated in wagons at the stations Sennaya Plochiad and Tekhnologuitcheski Institout".
President Vladimir Putin was scheduled to meet with Belarusian President Alexander Lukashenko in the city today. Chechen rebel leader Doku Umarov claimed responsibility for that attack by two female suicide bombers, warning Russian leaders that "the war is coming to their cities".
Passengers appeared to be fleeing the smoke-filled station.
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There have been incidents off the pitch as well, which have been making headlines throughout the series. Gilchrist said just like others he too was surprised by Australia's performance in the ongoing series.
Another bomb was deactivated at a separate St. Petersburg metro station shortly after the first blast, according to the Associated Press.
"The Moscow metro is taking up additional security measures in the framework of the federal law on Russia's transport security", a statement said.
Russia's anti-terrorism committee confirmed at least 10 people had been killed.
More than 310,000 people have been killed in Syria since the conflict broke out in March 2011 with protests against Assad's rule.
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Police said that Nelson suffered from multiple food allergies, but it is yet unclear what caused her death, the report said. He also went into the smoking World Trade Center to rescue workers during the 1993 bombing, despite having asthma.
Suicide bombings in the Moscow subway on March 29, 2010, killed 40 people and wounded more than 100 people.