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.

"A preliminary investigation shows that a man, his wife and their child were killed in the blast. The car driver has got wounds and is hospitalized," Interfax quoted a Russian secret services source as saying.

The source added that the blast looked to have resulted from a "grenade," without giving further details.

Vladimir Markin, a spokesman for Russia's top investigative committee, said a probe had been launched into the incident. (dpa)