Four people were hospitalized after a blast inside a store in the Russian city of St. Petersburg, state-run news outlet Tass reported Wednesday.
A total of 10 people were injured, the Russian state-run news agency Sputnik said.
Preliminary data shows that an explosive device found at the scene contained 200 grams (7 ounces) of TNT, state-run RIA news agency reported. The device was inside a locker at a chain supermarket called Perekrestok, located in an entertainment complex.
Tass reported that the Investigative Committee of the Russian Federation has opened a criminal investigation into the explosion, citing Svetlana Petrenko, an official representative for the committee.