US media say the country's intelligence had known in advance that the head of the Russian private military firm Wagner Group, Yevgeny Prigozhin, was planning a rebellion against Russia's defense ministry.

The Washington Post quoted US government sources as saying US intelligence detected signs of Prigozhin's plan in mid-June, and became increasingly concerned about its possible impact on Russia's ability to control its nuclear arsenal.

The article says Prigozhin's action was triggered by Russia's defense ministry's order on June 10 that all volunteer fighters participating in the Ukraine invasion must sign contracts with it to consolidate the chain of command.

It says Russian President Vladimir Putin likely knew about Prigozhin's plan, and that US officials surmised "Putin's inaction reflected a lack of high-level coordination in the Russian government and likely internal rivalries."