The leader of Russia’s Wagner mercenary group, Yevgeny Prigozhin, on Friday vowed to topple Russia’s military leadership, hours after the Kremlin accused him of armed rebellion, reported Reuters.

With Prigozhin’s warning on Friday, many believe that Russian President Vladimir Putin is faced with a domestic challenge of curbing a civil war. The development comes amidst Russia’s invasion of Ukraine. The private army of mercenaries has been fighting alongside the Russian army in Ukraine.

However, after the group captured the Ukrainian city of Bakhmut last month, which was Russia’s biggest victory in ten months, Prigozhin used the opportunity to criticise Kremlin, reported Reuters. Prigozhin had openly accused Russian Defence Minister Sergei Shoigu and the country’s top general, Valery Gerasimov, of incompetence.

On Friday, the mercenary leader accused the Russian military of launching a missile strike on his troops.

“Those who killed our lads, and tens of thousands of lives of Russian soldiers [in the war in Ukraine] will be punished,” he said in an audio message posted to the social media platform Telegram, reported the BBC. “I ask you not to resist. Anyone who does will be considered a threat and destroyed. That goes for any checkpoints and aviation on our way.”

On Friday, Wagner fighters had entered the southern Russian city of Rostov, after crossing the Ukrainian border, Prigozhin said in an audio recording posted on Telegram, reported BBC.

Meanwhile, Russia’s Federal Security Service has opened a criminal case against Prigozhin accusing him of “calling for an armed rebellion” and attempting to start armed civil conflict in Russia, reported TASS. Russia has also denied Prigozhin’s allegations of armed attack against his troops.

“Prigozhin’s statements and actions effectively constitute calls for an armed civil conflict on Russian territory and a stab in the back of Russian servicemen fighting with pro-Nazi Ukrainian forces,” the Federal Security Service said.

The deputy commander of Russia’s Ukraine campaign, General Sergei Surovikin, also urged the Wagner group to follow Putin’s order and resolve all issues peacefully, TASS reported.

“The enemy is waiting for our internal political situation to escalate,” Surovikin said. “We must not play in enemy’s favor in this difficult time. Before it is too late, it is necessary to submit to the will and order to the nationally elected president of the Russian Federation, to stop the convoys, to take them back to their permanent deployment and concentration locations, and to only resolve all issues peacefully.”

Security measures in Moscow have also been increased amidst Wagner’s offensive.