The head of the Russian mercenary group Wagner has vowed to take all necessary steps to topple the country's military leadership in Moscow, saying his forces would "destroy everything" in their way.
In a new audio message, mercenary chief Yevgeny Prigozhin said they will "go to the end", after vowing to sideline Russia's military leadership.
The White House has been following the situation in Russia since the call for an armed mutiny was made.
Russia accused Mr 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, the ministry issued a statement, saying Mr Prigozhin's accusations were "not true and are an informational provocation."
Mr Prigozhin said his actions did not amount to a military coup.
However, 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.
The Kremlin said President Vladimir Putin had been informed and that "necessary measures are being taken".
The standoff, many of the details of which remained unclear, looked like the biggest domestic crisis Mr Putin has faced since he sent thousands of troops into Ukraine in February last year in what he called "a special military operation."
Mr 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.
He also said 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, Mr 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."
Mr Prigozhin said his actions were "not a military coup", adding "most of the military support us fervently."
Unverified video
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 eyewitnesses, the strike was delivered from the rear, that is, it was delivered by the military of the Russian Ministry of Defence," it stated.
Moscow's National Anti-Terrorism Committee said that, following Mr 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.
Wagner spearheaded Russia's capture of the Ukrainian city of Bakhmut last month and Mr Prigozhin has used its battlefield success, achieved at enormous human cost, to publicly criticise Moscow with seeming impunity, until now.
He for the first-time dismissed Mr Putin's core justifications for invading Ukraine on 24 February 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," Mr Prigozhin said in a video clip.
"The war wasn't needed to demilitarise or denazify Ukraine," he said.
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 Mr 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," he added.
