"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.

"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 told journalists.

He 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.

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

Sweden's Foreign Minister Tobias Billstrom said the unrest was an "internal affair" for Russia.

He insisted that the "most important thing" was supporting Ukraine so it can win back its territory.