The shrapnel-laden homemade explosive device wounded at least 10 people in St. Petersburg, Russia's second city. Russia is on high alert for Islamist militant attacks.
At least 10 people were injured by an explosion at a supermarket in St. Petersburg on Wednesday, Russian officials said.
The blast was caused by a "homemade explosive device" with the power of 200 grams (7 ounces) of TNT, Investigative Committee spokeswoman Svetlana Petrenko said in a statement.
The nation's top investigative agency said the explosive device contained shrapnel and went off in a locker for customers' bags at a Perekrestok supermarket.
Investigators are looking at "all possible causes of what happened," Petrenko said.
Authorities refrained from labeling the explosion a terror attack. It is currently being treated as an "attempted murder."
None of those hurt sustained life-threatening injuries.
Russia on high alert for Islamist militant attacks.
St. Petersburg was hit by a metro bombing in April claimed by an al-Qaeda linked group. Fourteen people were killed and dozens more wounded.
Russia has become a target for Islamic extremists since itintervened militarily in Syria in September 2015, turning the tide of that country's civil war in favor of the Assad regime.
Several thousands of Russian citizens are believed to have gone to Syria to fight alongside the "Islamic State" (IS), al-Qaeda linked groups and other extremist outfits.
Earlier this month Russian President Vladimir Putin thanked US President Donald Trumpafter American intelligence provided information that foiled a planned terror attack in St. Petersburg.
Russia's FSB intelligence agency arrested seven suspected members of an IS cell and seized explosives and weapons before they could carry out the attack.
cw/jil (AFP, AP, dpa, Reuters)