Russian mercenary leader Yevgeny Prigozhin was on the passenger list of a jet which crashed in Russia killing all 10 people on board, Russias civil aviation authority says.
Social media linked to the Wagner mercenary group say his private plane was shot down by Russian air defences.
Prigozhin died "as a result of actions of traitors to Russia", the Grey Zone Telegram channel posted.
Prigozhin led an aborted mutiny against Russias armed forces in June.
However, some experts in Russia and abroad suggest the revolt was staged, and Prigozhin abandoned his "justice march" on Moscow after direct orders from President Vladimir Putin.