A surprising rebellion erupted in Russia on Friday, led by the head of the Wagner mercenary group, who accused the Russian military of targeting his Wagner forces in Ukraine with airstrikes and artillery even though they are meant to be fighting on the same side. 

The rebellion has triggered the gravest domestic crisis for Russian President Vladimir Putin since the Russia-Ukraine conflict broke out more than one year ago.

Yevgeny Prigozhin, the mercenary boss, has been a close ally of the president. He announced earlier that his Wagner fighters had left Ukraine and crossed the border into Russia's Rostov-on-Don, a southern city where Prigozhin said his forces had taken control of all military installations.

He also said he and his men were prepared to go "all the way" against Moscow's military and would destroy anyone who stood in their way.

The National Anti-Terrorism Committee, part of the Federal Security Service, or FSB, has charged Prigozhin with calling for an armed rebellion, punishable by up to 20 years in prison, and urged Wagner's contract soldiers to arrest Prigozhin and refuse to follow his "criminal and treacherous orders."

Putin called the rebellion treason and a "stab in the back" to Russia in a televised address to the nation on Saturday. He condemned the rebellion at a time when Russia was "fighting the toughest battle for its future" 

"The entire military, economic and information machine of the West is waged against us," Putin said, adding that anyone who had taken up arms against the Russian military would be punished, and that "decisive action" would be taken to stabilize the situation in Rostov-on-Don.

Read more: Live updates of the Wagner mutiny

Why the mutiny?

The head of Wagner has been in a feud with the Defense Ministry for years.

Over the past 16 months, he has frequently ranted against Russia's top military leaders, namely Sergei Shoigu, the defense minister, and General Valery Gerasimov, the head of Russia's armed forces, accusing them of incompetence over the military effort in Ukraine and of starving his troops of weapons and ammunition.

He also repeatedly criticized high-level corruption in the Russian military and accused Shoigu and Gerasimov of lying about battlefield situations to the president. He demanded that both of them take responsibility for setbacks in Ukraine and step down.

His latest act of defiance appears to have been triggered by what he claims to be attacks by the Russian military on his group. Prigozhin alleged that Wagner field camps in Ukraine were struck by rockets, helicopter gunships and artillery fire on orders from Gerasimov, following a meeting with Shoigu in Rostov at which they decided to destroy Wagner. 

The Defense Ministry denied the charge, and Russian officials also dismissed the video as fake, which was posted on a Wagner-linked channel purported to show the aftermath of an alleged Russian rocket attack against a Wagner camp in a forest.

Prigozhin said his rebellion is a punishment for Shoigu who ordered strikes against his forces and the march to Moscow "is not a military coup, but a march of justice," urging the army not to offer resistance.

Col. Gen. Sergei Surovikin, the deputy commander of the Russian group of forces fighting in Ukraine, urged the Wagner forces to stop any move against the army, saying it would play into the hands of Russia's enemies, who are "waiting to see the exacerbation of our domestic political situation."

Earlier this month, the mercenary chief brushed off an order from the defense minister who gave a directive for all "volunteer detachments" to sign contracts with the defense ministry by the end of the month, and that it's a step to increase the effectiveness of the Russian army fighting in Ukraine.

Prigozhin refused, alleging that the minister "cannot properly manage military formations" and that reporting to him will damage Wagner forces' high efficiency.

Prigozhin and his mercenary group

Prigozhin was convicted of robbery and assault in 1981, and sentenced to 12 years in prison. Following his release, he opened a restaurant business in St. Petersburg in the 1990s. It was in this capacity that he got to know Putin, then the city's deputy mayor.

Aside from his catering business, Prigozhin later expanded into other areas, including media. And in January, he acknowledged founding, leading and financing the Wagner company.

The Wagner Group is a private army of mercenaries that has been fighting alongside the regular Russian army in Ukraine. First identified in 2014, the group has backed pro-Russian separatist forces in eastern Ukraine and has grown considerably since. According to the U.S. National Council, about 80 percent of Wagner's troops in Ukraine have been drawn from prisons.

According to the AP, Wagner personnel were also deployed to Syria, Libya, the Central African Republic and Mali. Prigozhin has reportedly used Wagner's deployment to Syria and African countries to secure lucrative mining contracts. And U.S. Undersecretary of State Victoria Nuland alleged in January that the company was using its access to gold and other resources in Africa to fund Russia's military operations in Ukraine.

Public reports show that Russia's combat forces in Ukraine are various, including the federal force, which is Russia's official military force, security forces, which include the special force, anti-terrorism force, quick reaction force and the national guard team, pro-Russia militias, including those in the Donetsk and Luhansk regions, Chechen special forces, a paramilitary group led by the regional leader Ramzan Kadyrov, and the Wagner, a mercenary group that plays a crucial role in Russia's conflict with Ukraine, succeeding in taking the city where the bloodiest and longest battles have taken place, Bakhmut.

While the outcome of the current confrontation was still unclear, it appeared likely to hinder Moscow's military effort as Kyiv's forces were probing Russian defenses in the initial stages of a counteroffensive. The dispute, especially if Prigozhin were to prevail, also could have repercussions for Putin's government's ability to maintain a united front.

(With input from agencies)