The explosion occurred during a cleanup of one of the Besmen complexes on Friday when people were unloading garbage into a container, Xinhua news agency quoted the district's presidential office as saying.

The President's Office said the World War II-era 76-millimeter ammunition was "arbitrarily detonated."

According to the press office, the injured have been taken to a health facility of the Defense Ministry.

Saint Petersburg Governor Alexander Beglov denied that the incident was terrorist-related.