As one of the most brutal mercenary forces marched toward Moscow, some among Russia's elite trembled in fear that the world's biggest nuclear power was teetering on the brink of what President Vladimir Putin said could have been a civil war.

With Putin facing the biggest public challenge of his 23 years as paramount leader, some private jets sped out of Moscow, according to flight tracking data and one source with knowledge of the matter.

One fear was that Yevgeny Prigozhin's Wagner mercenary group, if they entered Moscow, would try to take over the economy, triggering yet another redistribution of ownership in Russia, the world's biggest supplier of natural resources.