Russian journalist Sergei Dorenko has died in Moscow, Russian media reported.
According to some reports, Dorenko lost consciousness as he was riding a motorcycle in the center of the capital.
TASS reported that he suffered a heart attack.
Earlier reports said he had been involved in a collision.
Dorenko, 59, was a prominent journalist in the 1990s and early 2000s. His weekly news program was canceled in 2000 shortly after it broadcast harsh criticism of the government's handling of the sinking of the Kursk nuclear submarine.
He did not work on Russian television again after that, but in recent years he had worked as editor in chief of the Govorit Moskva radio station.
He made headlines in 2007 when he released an interview that he had conducted in April 1998 with FSB officer Aleksandr Litvinenko and other FSB officers in which they confessed that they had been ordered to kill, kidnap, or blackmail prominent politicians and businesspeople.
Litvinenko died in London in 2006 of acute radiation poisoning.
British investigators established that he was poisoned with polonium 210 by Andrei Lugovoi, an officer of Russia's Federal Protection Service.
Lugovoi and the Russian government denied involvement in Litvinenko's killing.