MOSCOW, March 31 (RIA Novosti) - A seven-year-old boy accidently killed himself with a knife while pretending to be "a maniac" during a game with his friends in southern Russia's Rostov Region, investigators said on Tuesday.

Four small children were left without parental supervision in an apartment in the town of Novoshakhtinsk, when one of the children suggested playing a horror game, grabbed a kitchen knife and began chasing his friends.

"The other children rushed to shut the door just at the moment, when the child with the knife was running towards them," the source said. "As soon as the door shut, the children heard him crying."

The boy apparently hit the door while running and accidentally stabbed himself in the head. He later died in hospital.

An investigation is underway to decide whether a criminal case should be opened.