A blast ripped through a supermarket in the Russian city of St Petersburg on Wednesday evening, injuring several shoppers, Russian news agencies reported.
No one has claimed responsibility for the explosion at a branch of the Perekrestok supermarket chain in the city's northwest Kalininsky district.
"According to preliminary information, an explosion of an unidentified object occurred in a store", Investigative Committee spokesperson Svetlana Petrenko said in a statement.
Four people have been taken to hospital and six victims are being treated at the scene.
Just last week, Russian President Vladimir Putin thanked President Donald Trump and USA intelligence for a tip that led to the arrest of a suspected terrorist cell plotting bombings in St. Petersburg. "At the moment, the lives of those injured are not under threat".
The cause of the blast was not immediately known, but Russian news agencies reported that investigators had opened a criminal case on the grounds of attempted murder.
Local news sources said that officials are treating the explosion - equivalent to over 200g of TNT as deliberate.
Initial reports said that two bombs had gone off, but it became clear that there was a single blast - possibly in the third carriage of the train.
This isn't the first time Saint Petersburg has been targeted this year.