All claims of a military coup are absurd, claims Prigozhin.

But what began as a no-holds-barred row over the military's failure to supply his mercenaries with sufficient kit and ammunition has now spilled over into a direct challenge to the two men in charge of prosecuting the war - Defence Minister Sergei Shoigu and armed forces chief Valery Gerasimov.

So far this is not a coup, as there has been no stated bid to seize power from the government. Prigozhin's "private military company" does not represent the military either, although he does claim to have widespread support in the armed forces.

But it is an attempt to topple Russia's top brass and therefore a challenge to the president's authority. And even though it was Russia's leader who allowed Prigozhin to develop his rival force, he clearly has no control of him any more.

The Kremlin is taking this extremely seriously. The whole Moscow region has been put on an alert under a strict "counter-terrorist operation regime" and major events have been cancelled.