Russia claims that Yevgeny Prigozhin, the leader of Wagner, agreed to move to Belarus after the mercenary group gave up its rebellion.
Belarus also allowed Russian troops to invade Ukraine across its own border and to deploy Russian nuclear weapons on its territory.
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Where is Belarus and what kind of country is it?
Belarus is an Eastern European country surrounded by land on all sides and borders Russia and Ukraine.
It was a republic of the former Soviet Union until 1991.
Belarus has nine million inhabitants and is one of the poorest European countries.
Many parts of the economy are still state-owned.
In the past, it was often described as "the last European dictatorship".
Her government has been harshly criticized due to suppression of civil liberties and control of the media.
Its leader, Alexander Lukashenko, has been in power since 1994.
However, Great Britain, the EU and the USA no longer recognize him as president because they believe the elections were rigged.
The last presidential election in 2020 they caused several months of protests, which the security forces brutally suppressed.
The Kremlin has supported Lukashenko, offering to support his security forces and granting him an aid loan in the value of 1.5 billion dollars.
"Lukashenko has burned all bridges with the West and become isolated from his own people," says Dr. Nigel Gould-Davies, a former British ambassador to Belarus who is now a member of the International Institute for Strategic Studies think tank.
"That's why he became even more dependent on Russia."
How did Belarus help Russia with Wagner?
Lukashenko is tasked with being a mediator in the negotiations between Prigozhin and Russian President Vladimir Putin.
According to the Kremlin, Prigozhin retreated, his troops gave up their march on Moscow, and he agreed to move to Belarus after direct negotiations with Lukashenko.
However, Belarusian opposition leader in exile Svetlana Tikhanovskaya says that allowing Prigozhin to move to Belarus "adds a new element of instability" to the country, which does not need "more criminals and bandits".
How did Russia use Belarus to invade Ukraine?
In 2021, Belarus signed a security agreement allowing Russian troops to be deployed on its territory.
"Putin must have exerted a lot of pressure, because Lukashenko until then had consistently refused to accept Russian forces," says Emily Ferris of the Royal United Services Institute think tank.
In January and February 2022, Russian forces are held joint military exercises in Belarus, and then 30.000 Russian soldiers invaded Ukraine from its territory.
It was the shortest way to the Ukrainian capital of Kiev.
After the invasion, Belarus changed its status to a neutral and non-nuclear country.
It then allowed Russian forces to use its military bases, fire missiles from its territory, and use its rail and road networks.
In response, the UK, the EU, the US and Canada imposed sanctions on Belarus, just like Russia.
However, Lukashenko managed to ensure that Belarusian troops do not fight in Ukraine, says Oleg Ignatov from the International Crisis Group expert group.
"He is doing everything he can to avoid being involved in the war.
"It could be the last shred of legitimacy that Lukashenko has," he says.
What are the Russian nuclear weapons in Belarus?
In March, Russia deployed tactical nuclear missiles in Belarus to deter anyone "thinking about inflicting a strategic defeat on them."
Vladimir Putin, the Russian president, has said that some Iskander missiles, which can carry nuclear warheads, have already been transferred.
Tactical nuclear weapons contain small nuclear warheads designed to be used on the battlefield against specific targets.
Belarus has had no nuclear weapons on its soil since it agreed to remove them in 1994.
Speaking on Russian state television, Lukashenko said he not only allowed Russia to deploy nuclear weapons in Belarus, but "we demanded they be returned," he said.
"Putin didn't need to transfer these weapons to Belarus to attack Ukraine, but he may want more options to strike against targets in the West," says Dr Gould-Davies.
See how Yevgeny Prigozhin, the leader of the mercenary Wagner group, became a rebel
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