The device that blew up late Wednesday in Russia's second-largest city contained an explosive force equivalent to 200 grams of TNT, the National Anti-Terrorist Committee said in a website statement.
Fifty people were evacuated from the supermarket, at one of the busiest times of year after the blast, which fortunately killed no one. The bombing killed 14 people and injured nearly 50. The committee has opened a criminal investigation into "an attempt to kill two or more persons in a generally risky way".
"As of now, it has been established that 10 people were taken to the city's hospitals with injuries".
A police officer cordons off the site of a blast in a supermarket in Saint Petersburg on December 27, 2017.
Over a dozen people were murdered in the terrorist attack.
Russian President Vladimir Putin declared the explosion a terror attack
"What would have happened if those thousands [of terrorists] that I have just spoken about, hundreds of them had come back to us, trained and armed", Putin reportedly told Russian news agencies.
No-one has claimed responsibility for the explosion, which occurred at a branch of the Perekrestok supermarket chain in the city's north-west Kalininsky district.
Russia's National Anti-Terrorism Committee said it was coordinating the search for suspects, and a criminal investigation had been launched. "Emergency personnel are already on the scene".
It was reported that only a wall and a cash register inside the supermarket were damaged in the blast.
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