Below are what governments and analysts are saying about the extraordinary situation taking place in nuclear-armed Russia.

Ukraine

Ukrainian President Volodymyr Zelensky said that the Wagner mutiny showed Russia was weak.

"Russia's weakness is obvious. Full-scale weakness. And the longer Russia keeps its troops and mercenaries on our land, the more chaos, pain, and problems it will have for itself later," he said in statement on social media.

The Ukrainian army said Friday it was following infighting in Moscow after the head of the Wagner mercenary group accused Russia's military of attacking one of the private fighting group's bases.

"We are watching," the Ukrainian defence ministry tweeted, while Ukraine's military intelligence chief Kyrylo Budanov said rival Russian factions had begun to "eat each other over power and money."

The United States 

US President Joe Biden was briefed on the situation in Russia and Washington and "will be consulting with allies and partners on these developments", National Security Council spokesman Adam Hodge said.

Europe 

European Union chief Charles Michel tweeted that the bloc was "closely monitoring the situation in Russia as it unfolds. In touch with European leaders and G7 partners."

"This is clearly an internal Russian issue," he wrote, adding that "our support for Ukraine" remains "unwavering".

The bloc's diplomatic chief Josep Borrell said the EU was in "permanent contact with our ambassador in Moscow and continuing our internal consultations with our member states."

NATO spokesperson Oana Lungescu said only the alliance was "monitoring the situation".

British Prime Minister Rishi Sunak urged "all parties to be responsible and to protect civilians."

"We're in touch with our allies as the situation evolves. I'll be speaking to some of them later today and the most important thing is for all parties to behave responsibly," he told the BBC.

Meanwhile, Czech politicians used the mutiny as a moment to take a stab at Russian leadership.

"I can see my summer holiday in Crimea is approaching," said Foreign Minister Jan Lipavsky, referring to the territory annexed by Russia from Ukraine in 2014.

"So we finally know what the Russians mean by a Special Operation," said Czech Defence Minister Jana Cernochova.

"After 16 months of the war in Ukraine, Russia is waging war on Russia. No surprise. It's a tradition over there. Failed wars end up with the Tsar being executed, with chaos and with a civil war supervised by snoopers. Congratulations," she said.

Austrian Chancellor Karl Nehammer, who has met Putin since the launch of the Ukraine war, warned of the nuclear risks of the instability in Russia.

"The operations of the Russian Federations are always of the utmost importance, because the Russian Federation has a great potential for biological, chemical and nuclear weapons," he said.

In Berlin, "the government is closely following the events in Russia", a spokesman told AFP. The foreign ministry advised avoiding central Moscow and government and military buildings in the capital.

In Paris, French President Emmanuel Macron is also keeping a close eye, the Elysee said. "We remain focused on supporting Ukraine."

In Rome, Italian Prime Minister Giorgia Meloni's office said the events "show how the aggression against Ukraine is causing instability also within Russia."

In Sweden, Foreign Minister Tobias Billstrom tweeted: "The government is closely following the situation in Russia. The situation is serious."

In Norway, Foreign Minister Anniken Huitfeldt said Oslo was "closely following the dramatic situation in Russia and are in close contact with the embassy in Moscow."

Belgian Defence Minister Ludivine Dedonder tweeted that the situation was "serious" and he was watching to see "what impact it has on the conflict."

 Qatar

Qatar's foreign ministry said it was following "with great concern" and urged restraint.

"The worsening situation in Russia and Ukraine will have negative repercussions on international peace and security, and on food and energy supplies, which were mainly affected by the Russian-Ukrainian crisis," the ministry said.

Analysts 

The UK Ministry of Defence said in an intelligence update that "this represents the most significant challenge to the Russian state in recent times."

"Over the coming hours, the loyalty of Russia's security forces, and especially the Russian National Guard, will be key to how the crisis plays out," it said in a tweet.

The US-based Institute for the Study of War said the armed rebellion was "unlikely to succeed" but that "an armed Wagner attack against the Russian military leadership in Rostov-on-Don would have significant impacts on Russia's war effort in Ukraine."