Moscow/St Petersburg - A car exploded near a metro station in the Russian city of St Petersburg on Tuesday, killing three people, including a 3-year-old child.
Russian news agencies quoted law enforcement officials as saying the blast was caused by a grenade.
But St Petersburg police chief Vladislav Piotrovsky ruled out terrorism on Tuesday.
"There was no act of terrorism - the grenade just went off by accident. It is not clear yet why the man had a grenade," Piotrovsky was quoted by Interfax as saying.
"We will have a clearer picture by the end the end of day," he said.
The explosion occurred near the Udelnaya station at 8:55 am, an Emergency Situation Ministry spokesman said.