The UK prime minister is watching events closely, as the government holds an emergency planning meeting.
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Rishi Sunak has urged all sides in Russia to “be responsible and to protect civilians”, as mercenaries from the Wagner group seize military sites from Russia and Vladimir Putin vows to “punish” those involved in the move against his government.
In the UK, a meeting of the emergency committee, Cobra, was chaired by Foreign Secretary James Cleverly on Saturday afternoon.
We don’t get to hear much about what is said in those meetings, but the government says Mr Cleverly received all the latest information and particular attention was paid to the situation of British nationals still in Russia.
Mr Sunak has also spoken to US President Biden, French President Macron and German Chancellor Scholz about the situation.
Speaking exclusively to Sunday With Laura Kuenssberg, Mr Sunak suggested the government has been watching the internal threats to Vladimir Putin for some time.
He told me: “We have been monitoring for a while the potentially destabilising impacts of Russia’s illegal war in Ukraine.”
And he said the situation was “evolving on the ground as we speak”.
But he urged calm on all sides, saying: “The most important thing I’d say is for all parties to be responsible and to protect civilians”, a clear hint that the UK is concerned about how conflict inside Russia’s borders could spiral, when for months the focus has naturally been on fighting in Ukraine.
The prime minister did not repeat a more candid assessment from the Ministry of Defence, which said on its official Twitter feed that “this represents the most significant challenge to the Russian state in recent times”.
But Mr Sunak did not deny that was the case.
With so much unclear, it is evident that Number 10 does not yet want to give an official verdict on what is happening.
Yet it is clear from the Ministry of Defence’s comments that the government sees the action taking place as a potential game changer.
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The situation is volatile and no-one in Westminster would predict with any certainty what will happen next.
It is not clear exactly what Wagner chief Yevgeny Prigozhin’s motives are.
Nor is it certain how many resources and men Wagner really has at their disposal.
But one of the questions being asked in Westminster this afternoon is how Ukraine can make the most of what seems like disarray inside Russia to make progress in what is now a long-running conflict.
Our politicians, like the rest of us, are watching events and wondering what on earth is going on, and unable to be sure what will happen next. But they are watching with eager attention.
The war in Ukraine has had such enormous implications for politicians in the UK, because it has indirectly affected every family, every firm, and every household in the country by driving up the cost of energy.
That’s one of the biggest factors in high inflation the prime minister describes as the “number one enemy”.
We talk to the prime minister about that, his plans for the NHS and Boris Johnson in an exclusive interview you can watch on Sunday morning.
But as events unfold in Russia, remember that the actions of one man, Vladimir Putin, upended so much here.
Moscow may be nearly 2,000 miles away, but what happens in the next few days to stability in Russia matters hugely to our politicians in Westminster, and to us all.
