Wagner boss Yevgeny Prigozhin was on the passenger list of a plane which crashed in Russia, killing all 10 on board.
He was believed to be on board the plane.
Earlier, a Wagner-linked Telegram channel Grey Zone reported that the jet was shot down by air defences in Tver region, north of Moscow.
Prigozhin led a failed mutiny against the Russian armed forces in June.
Grey Zone said local residents heard two bangs before the crash and saw two vapour trails.
Tass news agency said the plane caught fire on hitting the ground, adding that four bodies had already been found.
The aircraft had been in the air for less than half an hour, it said.
The 62-year-old mercenary boss 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 move came after months of tension with Russian military commanders over the Ukraine conflict.
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, being seen in Russia and also reportedly visiting Africa.
But several Russia watchers have described him as a "dead man walking" since the mutiny.
President Putin's initial reaction to his challenge to Russia's defence establishment was vitriolic, calling it a betrayal and a stab in the back in a video message on 24 June.
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.
But given the circumstances any claims that his demise, if confirmed, was an accident will see a lot of eyebrows raised.
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