The head of the Wagner mercenary group, which in June attempted to topple Russia's military leadership, was on board a plane that crashed on Wednesday, with all passengers killed, Russian officials said.
The Kremlin and the defence ministry were yet to react.
Yevgeny Prigozhin's short-lived rebellion was seen as the biggest challenge to Russian President Vladimir Putin's authority since he came to power.
Since then, uncertainty has surrounded the fate of Wagner and its controversial chief.
Russia's ministry for emergency situations on Wednesday announced the crash of a private plane travelling between Moscow and Saint Petersburg.
According to preliminary information, all 10 people on board died, including three crew members, the ministry said.
Russia's aviation agency later said the Wagner chief was on board the plane.
"According to the airline, the following passengers were on board the Embraer-135 (EBM-135BJ) aircraft:... Prigozhin, Yevgeny," said Rosaviatsia, which also listed Dmitry Utkin, a shadowy figure who managed Wagner's operations and allegedly served in Russian military intelligence.
Telegram channels linked to Wagner posted footage -- that AFP could not independently confirm -- showing the wreckage of the plane burning in a field.
Russian law enforcement officials were standing guard at the crash site near the village of Kuzhenkino in the Tver region early on Thursday, AFP images showed.
In Saint Petersburg, people laid flowers and patches bearing the Wagner skull logo at a makeshift memorial outside the private mercenary group's headquarters, AFP journalists said.
"Guys, we just have no words right now," said a masked man and alleged members of Wagner at the site.
"Let's support Yevgeny Viktorovich (Prigozhin) and all our commanders. We need your support now."
Rosaviatsia said it set up a special commission to investigate the crash of the aircraft belonging to MNT-Aero.
Russia's Investigative Committee, which probes serious crimes, said it opened an investigation into the crash.
The bodies of eight people have been found so far at the site of the crash, RIA Novosti said citing the emergency services.
Putin was meanwhile giving a speech for the 80th anniversary of the Kursk battle in World War II.
He did not mention the crash and hailed "all our soldiers who are fighting bravely and resolutely" in the special military operation in Ukraine.
But Kyiv and Washington reacted swiftly to initial reports of the crash.
"I don't know for a fact what happened, but I'm not surprised," United States President Joe Biden said.
"There's not much that happens in Russia that (President) Putin's not behind. But I don't know enough to know the answer."