Information on the Wagner Group can be hard to come by, because it operates in the shadows.
Now, after an , the paramilitary organisation is very much in the spotlight.
Here's what we know.
Why has the Wagner Group been accused of treason?
On Friday, Wagner Group boss Yevgeny Prigozhin called for an armed rebellion and pledged to oust Russia's military leadership over their leadership of the war against Ukraine.
He had said he had 25,000 fighters moving from Ukraine towards Moscow to "restore justice" and vowed he and his men would destroy anyone who stood in their way.
The Wagner Group has been a known presence in Russia's war against Ukraine and has been connected to conflicts in Africa. Now, it's been accused of treason by Vladimir Putin. Credit: TASS/Sipa USA
Russia's security services have called for his arrest, and accused Mr Prigozhin of an "armed mutiny".
In an emergency address on Saturday, Mr Putin said those involved were "traitors" and would be punished.
"It is a blow to Russia, to our people. And our actions to defend the Fatherland against such a threat will be harsh," he said.
"All those who deliberately stepped on the path of betrayal, who prepared an armed insurrection, who took the path of blackmail and terrorist methods, will suffer inevitable punishment, will answer both to the law and to our people."
He described the situation as "treason" and a "stab in the back".
What do we know about the Wagner Group?
The Russian paramilitary organisation has been accused of human rights abuses, war crimes, unlawful killings and gold smuggling. It allegedly has close links to the Russian state and Vladimir Putin.
It is known to operate in Russia and Ukraine, where it commands 50,000 fighters and has become a key component of the Russian campaign, according to the UK Ministry of Defence.
A former Wagner commander in Ukraine Andrey Medvedev earlier this year. He says he witnessed several war crimes, including deserters being executed by the Wagner Group while fighting in Ukraine's eastern Donbas region.
In this still from a video released on 3 March 2023, Yevgeny Prigozhin addresses Ukrainian President Volodymyr Zelenskyy, asking him to withdraw the remaining Ukrainian forces from Bakhmut to save their lives, at an unspecified location in Ukraine. Source: AAP / AP
Who is Yevgeny Prighozin?
Russian billionaire Yevgeny Prighozin, sometimes described as "Vladimir Putin's chef", was long-suspected to be the organisation's founder before ending years of denial in September 2022, when he acknowledged he had set up the group in 2014.
He owns a network of restaurants and companies, and has been involved in Moscow leadership for decades,
In recent months he has openly feuded with Russian generals about their war strategies.
Wagner has also been a known presence in several African countries, where it is linked to mining and infrastructure projects and has been accused by companies owned by Mr Prighozin – M Invest and a subsidiary group, Meroe Gold – as fronts "to evade sanctions and transact in US dollars despite being blocked from the US financial system".
The group's name has popped up in relation to recent conflict in Sudan, which has triggered a humanitarian crisis, killed over 500 people, and left millions of Sudanese people without access to basic services. The crisis is primarily driven by conflict between the nation's army and the paramilitary Rapid Support Forces (RSF).
What are the Wagner Group doing in Sudan?
International observers have been speculating on what exactly the Wagner Group's role in Sudan is, with some media outlets alleging that the group are supplying weapons for the conflict. Others have pointed out that the Wagner Group has previously been involved in mining operations in Sudan.
Mr Prighozin has said that "not a single Wagner fighter has been present in Sudan" for over two years.
But Isabella Currie, who researches the group at La Trobe University, says his public messaging has been confusing, misleading, and wrong in the past.
"That denial is just not really something that we can take as truth – what Prighozin is saying, and what is the actual truth and what's happening, are often two contradictory things."
However, she says instability in Sudan wouldn't necessarily be in the Wagner Group's interests.
"What we do know is that Hemadti, who is really the leader of the RSF, has been the beneficiary of training and resources in the past. And so, if he has been receiving support from Wagner, it's probably going to be a continuation of a pre-established relationship," she said.
How connected is Wagner Group to the Kremlin?
Ms Currie says the relationship between the Kremlin and the Wagner Group has ebbed and flowed over the last nine years.
"There has been major evidence that suggests that the Wagner group has functioned as an extended arm of the military and security forces of Russia.
But over the last 12 months, there's been micro-conflicts and even quite a bit of competition between the Wagner Group and the military and security forces in Russia," she said.
There are some researchers who argue that Wagner has some contacts with the Russian government, but in general is its own entity. Others say it is just a front group for the Russian government.
A badge is pictured on a uniform of a Wagner Group soldier in the city of Bakhmut. Source: AAP / TASS/Sipa USA
"The number one reason the Kremlin would work with mercenaries is so they have some plausible deniability," he said.
"They can say, when they're confronted with some of the crimes committed by Wagner in Ukraine, they don't have any responsibility for those actions."
Mr Kłyszcz said that, because of this plausible deniability argument, the Wagner Group can be much more brutal and inhumane than official armies, both on the ground and in its recruitment.
The United Nations has condemned the Wagner Group's alleged policy of recruiting prisoners, who are believed to make up a large percentage of troops in Ukraine.
International lawyers are very interested in Wagner's relationship with the Russian government. If it's determined that the government exerts some control on the group, the former could be held responsible for their actions.
Because of the Wagner Group's status as private actors, and the lack of an international framework to deal with such mercenary groups, they may be difficult to stop.
But Ms Currie says shining a light on the group through research could go some way to hampering their operations.
"With more attention and more of a focus on where they are, they may find it more challenging to secure contracts, because there's a heightened focus on what they might look to next," she said.
What does the Kremlin want to achieve in Africa?
The non-government organisation Global Initiative Against Transnational Organised Crime says Russia's most significant presence in Africa is not the Russian state, but the Wagner Group.
Mr Kłyszcz said that, from a foreign policy perspective, the current clashes in Sudan advance Russia's broader, anti-democratic agenda.
"Russia's foreign policy objectives are to protect its regime. So to do that, it needs to delegitimise democratic revolutions and democracy overall, so the failure of the Sudanese transition is in the Kremlin's interest," he said.
US Intelligence documents state that Russia, supported by the Wagner Group, is working to establish an anti-Western and specifically anti-French confederation of states in at least eight African countries.
Russia also has interests in Sudan as a naval destination. When Sudan's former leader Omar al-Bashir was in conflict with the US, he began to lean more on Russia. In 2017, he travelled to Moscow and made an agreement allowing Russia to operate a military naval installation on Sudanese ground.
Mr Kłyszcz said this was a very interesting proposition for Russia.
"Russia had been attempting to rebuild some sort of presence on the Red Sea for many years now. So eventually, this Port Sudan opportunity came up.
"I've been very sceptical that it would ever amount to anything ... because the central government in Sudan was unable really to fulfil the terms of the agreement, namely to give conditions for Russia to install itself."
Where else are the Wagner Group active?
They have business operations in the Central African Republic that are thought to be linked to their presence in Sudan.
The United Nations condemned the violent harassment and intimidation of civilians, including peacekeepers, journalists, aid workers and minorities in the Central African Republic by Wagner Group members in 2021.
Wagner Group mercenaries have been in Syria since 2015, fighting alongside pro-government forces and guarding oilfields.
They are also in Libya, supporting the forces loyal to General Khalifa Haftar, and in Madagascar.
With additional reporting by Reuters.
