The youngster, considered one of Russia's best prospects and a hope for an Olympic medal at Rio 2016, was reportedly found dead in a Moscow hotel room last Thursday (November 26).

He had reportedly suffered sudden heart failure and was buried at a cemetery in St Petersburg on Sunday (November 29), according to Russian news agency TASS.

"Modern Pentathlon Federation of Russia is sad to announce that on November 26, Russian pentathlete Alexander Kukarin died," said a statement from the country's governing body.

"Modern Pentathlon Federation of Russia expresses condolences to the families and friends of the athlete."

Kukarin won relay silver with Kirill Belyakov at this year's World Championships in Berlin, and he also won a mixed relay bronze with Donata Rimshayte at the European Championships in Bath in August.

"We did not find any signs that he had been attacked, while there were no suspicious signs," the Modern Pentathlon Federation of Russia added in their statement.

"The athletes have finished their season and Alexander was not at a training camp.

"An unexpected cardiac arrest is our initial diagnosis.

"The autopsy and final results will be ready in one and a half to two months."

A statement from the International Modern Pentathlon Union said that it was too early for comment.

"We are still waiting for further information from the Russian Modern Pentathlon Federation about the sad facts that led to Alexander Kukarin's passing away," a spokesman for the world governing body said.