The Russian authorities on Saturday accused the head of the Wagner mercenary group of trying to start a "civil conflict" and called for his detention.
The FSB security service`s probe into calls to stage an "armed mutiny" came after Wagner chief Yevgeny Prigozhin, 62, accused Moscow of targeting his forces with deadly missile strikes and vowed to retaliate.
Mr. Prigozhin, 62, urged 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.
Rarely has such a controversial figure shot to this degree of prominence on the Russian political stage under Mr. Putin.
`Putin`s chef`
Mr. Prigozhin rose from a modest background to become part of the inner circle around the Russian leader.
He spent nine years in prison in the final period of the Soviet Union 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 St Petersburg whose customers included Mr. 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 Mr. Prigozhin the soubriquet of "Putin`s chef".
While Mr. 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 spilt onto the battlefield.
"They (Russia`s military) conducted missile strikes at our rear camps. A huge number of our fighters, our comrades died," he said in a series of furious audio messages released by his spokesmen.
"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 did not give the exact location of the alleged strikes or the number of victims. AFP could not independently verify the claims.
He has also accused the Russian military of attempting to "steal" victories in Ukraine from his forces, and slammed Moscow`s "monstrous bureaucracy" for slowing military gains.
`Provocation`
Mr. Prigozhin has repeatedly blamed Defense Minister Sergei Shoigu and General Valery Gerasimov, chief of the general staff, for his fighters` deaths on the battlefield.
The Russian defense ministry denied Mr. 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.
On Friday, Mr. Prigozhin said Moscow`s forces were retreating in Ukraine`s east and south following the start of Kyiv`s counter-offensive early this month. That directly contradicted Mr. Putin`s account that Ukraine was suffering "catastrophic" losses and that there was a lull in fighting.
"We are washing ourselves in blood," Mr. 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.
Questioning military operation
After years of operating in the shadows, Mr. Prigozhin has now admitted to running the elusive mercenary group and even interfering in US elections.
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.
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."
