Wagner boss Yevgeny Prigozhin was on the passenger list of a plane which crashed in Russia, killing all 10 on board according to Russia’s Civil Aviation authorities.
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.
Yevgeny Prigozhin led a failed mutiny against the Russian armed forces in June over the handling of the War in Ukraine.
The crash comes on the same day that senior Russian general Sergei Surovikin was reportedly sacked as air force chief.
Gen Surovikin was known to have good relations with Prigozhin and had not been seen in public since the mutiny.
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.
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, Ria, said eight bodies had been recovered.
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.
Prigozhin headed the mutiny on 23-24 June, moving his troops from Ukraine, seizing the southern Russian city of Rostov on Don, and threatening to march on Moscow.
The stand-off was settled by a deal which allowed Wagner troops to move to Belarus or join the Russian army.
Prigozhin himself agreed to relocate to Belarus but has apparently been able to move freely, making public appearances in Russia and releasing a video of him purportedly in Africa.
But several Russia watchers have described him as a “dead man walking” since the mutiny.
The deal did not mean he was safe.
“Revenge”, commented CIA director William Burns, “is a dish Putin prefers served cold” – or words to that effect.
None of this, of course, is proof that Prigozhin and his entourage were deliberately targeted.
US President Joe Biden said he was “not surprised” by news of Prigozhin’s possible death.