The Wagner group alleged that Russia's military conducted missile strikes at its rear camps.
Russian authorities on Friday opened a criminal probe into calls to stage an "armed mutiny" after the chief of the Wagner mercenary group accused Russia of targeting his forces with deadly missile strikes and vowed to retaliate.
Yevgeny Prigozhin, 62, called on Russians to join his forces and punish Moscow's military leadership in the most audacious challenge to President Vladimir Putin since the start of the offensive in Ukraine last year.
The Kremlin said Putin had been informed of Prigozhin's claims and "necessary measures are being taken," while the FSB security service opened a criminal probe into calls to stage an "armed mutiny."
While Prigozhin's private military outfit has spearheaded much of Russia's offensive in Ukraine, he has in recent months engaged in a bitter feud with Moscow's military leadership that he alleges has now spilled onto the battlefield.
"They (Russia's military) conducted missile strikes at our rear camps. A huge number of our fighters, our comrades died," Prigozhin said in a series of furious audio messages released by his spokespeople.
"The council of commanders of PMC Wagner has made a decision -- the evil that the military leadership of the country brings must be stopped."
He warned Russians against resisting his forces and called on them to join him, adding "there are 25,000 of us".
"Anyone who puts up resistance -- we will consider this is a threat and destroy immediately. Including any roadblocks on our way," he said.
"We need to put an end to this mess," he said, adding "this is not a military coup, but a march of justice."
He has repeatedly blamed Defence Minister Sergei Shoigu and Valery Gerasimov, chief of the general staff, for his fighters' deaths on the battlefield.
The Russian defence ministry on Friday denied Prigozhin's claims of an attack on his forces, saying the statements "do not correspond to reality", and calling them a "provocation".
"The Russian armed forces continue to carry out combat missions" in Ukraine, the ministry added.
"We demand that illegal actions be immediately halted," said Russia's National Anti-Terror Committee.
- 'Washing ourselves in blood'-
Earlier on Friday, Prigozhin said Moscow's forces were retreating in Ukraine's east and south following the start of Kyiv's counteroffensive early this month. That directly contradicted Putin's account that Ukraine was suffering "catastrophic" losses and that there was a lull in fighting.
"We are washing ourselves in blood," Prigozhin said.
"No one is bringing reserves. What they tell us is the deepest deception," he added, referring to the Russian military and political leadership.
After years of operating in the shadows, Prigozhin has now admitted to running the elusive mercenary group and even interfering in US elections.
His forces, bolstered by tens of thousands of prison recruits, played a central role in Russia's capture of the town of Bakhmut in the eastern region of Donetsk, the longest and bloodiest battle of the conflict.
However, this week he accused Moscow's top brass of deceiving Russians about the offensive in Ukraine.
"Why did the special military operation begin?" he said. "The war was needed for the self-promotion of a bunch of bastards."
Rarely has such a controversial figure shot to this degree of prominence on the Russian political stage under Putin.
- 'Putin's chef -
Prigozhin rose from a modest background to become part of the inner circle around Putin.
He spent nine years in prison in the final period of the USSR after being convicted of fraud and theft. In the chaos of the 1990s, he began a moderately successful business selling hot dogs.
From there he fell into the restaurant business and opened a luxury location in Saint Petersburg whose customers included Putin, then making the transition from working in the KGB to local politics.
The catering company he founded at one point worked for the Kremlin, earning Prigozhin the soubriquet of "Putin's chef".
However, in recent months, Prigozhin has become embroiled in a bitter power struggle with the defence ministry.
He has accused the Russian military of attempting to "steal" victories in Ukraine from his forces, and slammed Moscow's "monstrous bureaucracy" for slowing military gains.
Wagner's presence has been reported in conflict zones including Syria, Libya, Mali, and the Central African Republic, where it has been accused of abuses and capturing state power.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)