The owner of the Wagner private military group on Friday called for an armed rebellion against Russia's Defense Minister.
Yevgeny Prigozhin claimed his mercenary forces had reached the Russian city of Rostov without resistance.
"We will destroy anyone who stands in our way,” he warned. “We are moving forward and will go until the end."
Prigozhin said Russian military forces had struck against Wagner convoys and against Wagner field camps in Ukraine, on orders from Russia's Chief of General Staff, Gen. Valery Gerasimov.
Russia's National Anti-Terrorism Committee said it would investigate Prigozhin on charges of calling for armed rebellion. It called on Wagner forces to refuse to follow Prigozhin's orders, and to arrest him.
Russia's Lt. Gen. Vladimir Alexeyev said of Prigozhin's claims, "It’s impossible to imagine a stronger blow to the image of Russia and its armed forces. Such a provocation could only be staged by enemies of Russia."
1,000 Fighters From Putin's 'Shadow Army,' Wagner Group, Enter Ukraine
Experts expect the Wagner Group will supplement Russia's military forces in Ukraine as the invasion continues.
Wagner forces were instrumental in taking the city of Bakhmut in Ukraine for Russia, where some of the fiercest fighting of the war took place. Prigozhin recently accused Russia of not adequately supplying Wagner forces with enough munitions for the fighting there.
The Wagner Group emerged in 2014 in Ukraine, where it helped Russia annex Crimea. Since then it has reportedly been involved in conflicts worldwide, usually assisting Russia's military or Russian political interests.
The Kremlin denies any connection to the group.
