Wagner group boss Yevgeny Prigozhin, was on the passenger list of a jet which crashed killing all on board, Russia's civil aviation authority said on Wednesday.
Earlier, Wagner-linked Telegram channel Grey Zone reported that the private plane, which belonged to the 62-year-old, was shot down by air defences.
Grey Zone posted later on Wednesday that Prigozhin died "as a result of actions of traitors of Russia".
Prigozhin led a failed mutiny against the Russian armed forces in June.
The crash comes on the same day that senior Russian general Sergei Surovikin was reportedly sacked as air force chief, BBC reported.
Gen Surovikin was known to have good relations with Prigozhin and had not been seen in public since the mutiny.
The aircraft was flying from Moscow to St Petersburg, with seven passengers and three crew.
It is said to have come down near the village of Kuzhenkino in Tver region, about half-way between Moscow and St Petersburg.
Grey Zone said local residents heard two bangs before the crash and saw two vapour trails.
Tass news agency said the plane, an Embraer Legacy belonging to Prigozhin, caught fire on hitting the ground.
The aircraft had been in the air for less than half an hour, it added.
Senior Wagner commander Dmitry Utkin was also on the passenger list, aviation officials said.
An investigation has been launched into the crash and emergency services are searching the scene.
Another news agency, Interfax, said all 10 bodies had been recovered.
Grey Zone reported that a second business jet owned by Prigozhin landed safely in the Moscow region.
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