Wagner boss, Yevgeny Prigozhin is presumed dead after he was said to be on the passenger list of a jet which crashed killing all on board.
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 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.
An investigation has been launched into the crash and emergency services are searching the scene.
The mercenary boss founded Wagner in 2014, and it now has about 25,000 fighters.
The group has been active in Ukraine, Syria and west Africa, and has gained a reputation for brutality.
