Russia has accused Wagner mercenary chief Yevgeny Prigozhin of calling for an armed mutiny after he alleged, without providing evidence, that the military leadership had killed 2,000 of his fighters and vowed to stop what he called its "evil".
As a long-running standoff between him and the Defence Ministry appeared to come to a head on Friday, the ministry issued a statement, saying Prigozhin's accusations were "not true and are an informational provocation."
Prigozhin said his actions did not amount to a military coup. But Russia's Federal Security service [FSB] opened a criminal case against him for calling for an armed mutiny, the TASS news agency said, citing the National Anti-terrorism Committee.
Moscow's National Anti-Terrorism Committee said that, following Prigozhin's statements, the FSB had "initiated a criminal case based on calls for an armed rebellion", the state news agency RIA Novosti reported.
"We demand that illegal actions be stopped immediately," the committee added.
Russia's FSB accused Prigozhin of attempting to launch a "civil conflict" and urged his fighters to detain him, according to a statement carried on Saturday by Russian news agencies.
"[Yevgeny] Prigozhin's statements and actions are in fact a call to start an armed civil conflict on the territory of the Russian Federation and a stab in the back to Russian servicemen fighting pro-fascist Ukrainian forces," the statement said, urging Wagner fighters to "take measures to detain him".
Russia's Ukraine campaign, General Sergei Surovikin, urged Wagner fighters to give up their opposition to the military leadership and return to their bases.
"I urge you to stop. The enemy is just waiting for the internal political situation to worsen in our country. Before it is too late, it is necessary and it is needed to obey the will and order of the popularly elected President of the Russian Federation," Surovikin, commander of Russia's aerospace forces, said in a highly unusual video.
The Kremlin said President Vladimir Putin had been informed and that "necessary measures are being taken".
Meanwhile, the Ukrainian army said it was following infighting in Moscow.
"We are watching," the Ukrainian Defence Ministry tweeted, while Ukraine's military intelligence chief Kyrylo Budanov said rival Russian factions had begun to "eat each other over power and money."
Biggest domestic crisis for Putin
The standoff, many of the details of which remained unclear, looked like the biggest domestic crisis Putin has faced since he sent thousands of troops into Ukraine in February last year in what he called "a special military operation."
Prigozhin, whose frequent tirades on social media belie his limited role in the war as head of the Wagner private militia, has for months been openly accusing Defence Minister Sergei Shoigu and Russia's top general, Valery Gerasimov, of rank incompetence and of denying his forces ammunition and support.
But earlier on Friday, he had appeared to cross a new line in his increasingly vitriolic feud with the Defence Ministry, saying that the Kremlin's rationale for invading Ukraine was based on lies concocted by the army's top brass.
Then, in a series of late evening audio messages on his official Telegram channel, Prigozhin said: "The minister of defence has ordered 2,000 bodies that are being stored to be hidden so as not to show the losses."
He added: "Those who destroyed our lads, who destroyed the lives of many tens of thousands of Russian soldiers, will be punished. I ask that no one offer resistance ...
"There are 25,000 of us and we are going to figure out why chaos is happening in the country."
Prigozhin said his actions were "not a military coup", but added: "Most of the military support us fervently."
Unverified video on Telegram
An unverified video posted on a Telegram channel close to Wagner showed a scene in a forest where small fires were burning and trees appeared to have been broken by force. There appeared to be one body, but no more direct evidence of any attack.
It carried the caption: "A missile attack was launched on the camps of PMC (Private Military Company) Wagner. Many victims.
According to witnesses, the strike was delivered from the rear, that is, it was delivered by the military of the Russian Ministry of Defence."
Wagner spearheaded Russia's capture of the Ukrainian city of Bakhmut last month, and Prigozhin has used its battlefield success, achieved at enormous human cost, to publicly criticise Moscow with seeming impunity — until now.
But on Friday he for the first time dismissed Putin's core justifications for entering Ukraine on February 24 last year.
"The war was needed ... so that [Defence Minister Sergei] Shoigu could become a marshal ... so that he could get a second 'Hero' [of Russia] medal," Prigozhin said in a video clip. "The war wasn't needed to demilitarise or denazify Ukraine."
Marat Gabidullin, a former Wagner commander who moved to France when Russia invaded Ukraine, told Reuters that Wagner's fighters were likely to stand with Prigozhin.
"We have looked down on the army for a long time ... Of course they support him, he is their leader," he said.
"They won't hesitate [to fight the army], if anyone gets in their way."