At least ten people were wounded on Wednesday when a homemade bomb went off in a supermarket in the Russian city of St. Petersburg, investigators said. Nobody was killed in the explosion, and it was not immediately clear what the motive for it was. The bomb was packed with pieces of metal and had a force equivalent to 200 grams of TNT, they said. They have opened a criminal case on the grounds of attempted murder. Russian media reports said the bomb had been hidden in a locker where shoppers leave their belongings in a branch of the Perekrestok supermarket chain. “All possible versions of what has happened are being worked on,” Alexander Klaus, the head of St. Petersburg’s investigative committee, told Reuters. “As of now, it has been established that 10 people were taken to the city’s hospitals with injuries. At the moment, the lives of those injured are not under threat.” Viktoria Gordeyeva, a local resident who walked past the supermarket shortly after the explosion, said people feared entering other stores in the area after the blast. She added: "There was no panic, but people were reluctant to enter a nearby drug store and a grocery store." Russian President Vladimir Putin telephoned US President Donald Trump earlier this month to thank him for a CIA tip that helped thwart a series of bombings in St. Petersburg. The Federal Security Service, or FSB, said seven suspects linked to the ISIS group were arrested in connection to the alleged plot.