A mercenary group on Saturday claimed it has taken control of the southern Russian city of Rostov in an attempt to oust the country’s military leadership, Reuters reported.

Videos shared on social media showed members of the Wagner mercenary group at the headquarters of Russia’s Southern Military District in Rostov.

The group’s leader, Yevgeny Prigozhin, posted a video of himself at the headquarters and claimed that his forces are in control of the airfield and other military facilities in the city, according to the Associated Press.

The city serves as the main logistical hub for the Russian military in the war against Ukraine. The private army of mercenaries has been fighting alongside the Russian army in Ukraine.

Last month, the group had captured the Ukrainian city of Bakhmut, which was Russia’s biggest victory in ten months. Prigozhin had used the victory to accuse Russian Defence Minister Sergei Shoigu and the country’s top general, Valery Gerasimov, of incompetence, reported Reuters.

On Friday, Prigozhin vowed to topple Russia’s military leadership, hours after the Kremlin accused him of armed rebellion. He had also accused the Russian military of launching a missile strike on his troops, according to the BBC.

“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. “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.”

With Prigozhin’s warning, many believe that Russian President Vladimir Putin is faced with the domestic challenge of curbing a civil war. Security measures have been increased in Moscow amidst Wagner’s offensive, according to Reuters.

On Saturday, Putin said that he has given “necessary orders” to tackle the Wagner group with decisive measures to retake the city of Rostov.

“What we are dealing with is treason,” Putin said in a televised address. “Unchecked ambitions and personal interests have brought about betrayal to our country and our people.”

The Russian president also drew a comparison of the situation with the Russian Revolution in 1917 when the Tsar, or monarch, was overthrown and the Bolsheviks took power following widespread popular unrest.

“Russians were killing Russians and brothers were killing brothers, while all sorts of political adventurers and foreign forces profited from the situation by tearing the country apart to divide it,” he said. “We will not allow this to happen again. We will protect our people and our statehood from any threats, including from internal betrayal.”

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