Russia's National Antiterrorism Committee (NAK) is leading an investigation into a blast that injured at least 10 people at a supermarket in the Russian city of St. Petersburg.
While stopping short of calling it a terrorist attack, the committee confirmed it was taking charge of the probe in to the explosion that occurred at 6:45 p.m. local time on December 27 in a customer locker area at the city's Perekrestok supermarket.
"The NAK operations command is coordinating the activities of emergency services and law-enforcement agencies," the committee's press office said. "The search for those involved in the crime is under way."
Earlier, Russian Investigative Committee spokeswoman Svetlana Petrenko said that "a homemade explosive device with the power equivalent to 200 grams of TNT filled with lethal fragments went off" in the busy shopping area.
Petrenko did not mention terrorism in her comments, only that the authorities were "looking into every theory of the incident" and that, for now, the case was being classified as "attempted murder."
Officials said nine of the 10 injured in the blast had been sent to the hospital for treatment. At least one person was in serious condition and one other had been released.
Dozens of people were evacuated from the building. Footage on social media shows multiple police vehicles, ambulances, and fire engines outside the Gigant Hall leisure center, where the supermarket is located on the ground floor.
"There was a bang. Emergency personnel are already on the scene. The evacuation has been completed, and there was no fire," a local Emergency Situations Ministry official told TASS news agency.
The blast comes after the FSB on December 15 said it had arrested seven suspected Islamic extremists and thwarted plans for bomb attacks in St. Petersburg on December 16.
After the arrests, President Vladimir Putin telephoned U.S. President Donald Trump to thank him for a CIA tip that reportedly helped prevent the bombings in Putin's home town, including an alleged plan to bomb the Kazan Cathedral and other crowded sites.
The authorities are heightening security in the city, which is to be one of the hosts of the 2018 World Cup soccer championships running June 14 to July 15 in Russia.