"What has happened during this weekend shows that the war against Ukraine is cracking Russian power and affecting its political system," EU foreign policy chief Josep Borrell said at a meeting of the bloc's foreign ministers.

"We are certainly following closely what's happening, but it's now the moment to continue supporting Ukraine more than ever, that's what we will do," he said.

"Certainly it's not a good thing to see that a nuclear power like Russia can go into a phase of instability. It's also something that has to be taken into account," Borrell said.

"The most important conclusion is that the war against Ukraine launched by (Russian President Vladimir) Putin, and the monster that Putin created with Wagner, the monster, is biting him."

"The monster is acting against its creator, the political system is showing the fragilities and the military power is cracking," Borrell said.

- 'Fault lines' -

EU foreign ministers were scrambling to digest the fallout from the uprising at their regular meeting in Luxembourg.

Germany's Foreign Minister Annalena Baerbock said the events were "a domestic power struggle in Russia, and we are not getting involved".

"We see the devastating consequences of the Russian war of aggression, also on the power system of Putin," she said.

"We see that more and more Russia's leadership is striking back at itself."

French Foreign Minister Catherine Colonna said the tensions showed the "fractures and fault lines" in the Russian system.

But she said the EU was remaining "cautious" and did not want to be seen to interfere.

Lithuania's Foreign Minister Gabrielius Landsbergis urged the West not to be "distracted" and to focus on bolstering support for Ukraine.

"We don't need to think about changing the regime in Russia and the need to plan it; Russians are completely capable of doing that on their own," he said.

The foreign ministers meeting in Luxembourg formally approved adding another 3.5 billion euros ($3.8 billion) to a fund used to arm Ukraine.

But Hungary is currently blocking the allocation of an additional 500 million euros from the joint fund specifically to cover the costs of weapons sent to Kyiv.

Since the start of Russia's invasion in February 2022, the EU's 27 nations have already committed 3.6 billion euros from the shared European Peace facility to equip Ukraine's military.

The bloc has also been training thousands of Ukrainian troops for the fight against Moscow's forces.

Borrell said that the target of training 30,000 Ukrainian troops this year would be reached well ahead of schedule, and that the programme would be extended.