US, allies not involved in uprising against Putin: Biden

President Joe Biden on Monday said a brief uprising by Russian mercenaries against the Kremlin was part of a struggle within the Russian system and that the United States and its allies were not involved in it.

Biden offered a cautious assessment of unfolding events in an attempt to avoid inflaming tensions with nuclear-armed Russia while he offered firm Western support for Ukraine in its bid to turn back Russian invaders.

"We made clear we were not involved, we had nothing to do with this," Biden said in his first comments on the uprising by Wagner mercenaries that fizzled over the weekend.

Biden's message that the West was not involved was sent directly to the Russians through various diplomatic channels, White House national security spokesperson John Kirby told reporters. He did not characterize Russia's response.

At a White House event, Biden addressed the dramatic power struggle that erupted when the mutineers barreled toward Moscow only to stop before reaching the capital.

Biden said he had directed his national security team to update him on the situation "hour by hour" and to prepare for a range of scenarios, which he did not detail.

Russian intelligence services were investigating whether Western spy agencies played a role in the aborted mutiny, the TASS news agency quoted Foreign Minister Sergei Lavrov as saying on Monday.

The U.S. intelligence community "was aware" that the mutiny orchestrated by Wagner chief Yevgeny Prigozhin's "was a possibility" and briefed the U.S. Congress "accordingly" before it began, said a source familiar with the issue, who spoke on condition of anonymity.

The Biden administration would not address a widely held perception in Washington that the uprising showed that Russian President Vladimir Putin has been weakened by his 16-month war against Ukraine.

State Department spokesperson Matt Miller told reporters it is as yet unclear what the ultimate implications of what happened will be, but he noted: "It is a certainly a new thing to see President Putin's leadership directly challenged. It is a new thing to see Yevgeny Prigozhin directly questioning the rationale for this war and calling out that the war has been conducted essentially based on a lie."

Biden said he spoke with key allies on a video conference to make sure everyone was on the same page and coordinated in their response.

"They agreed with me that we had to make sure that we gave Putin no excuse - gave Putin no excuse - to blame this on the West and blame this on NATO," he said.

Biden, who spoke to Ukraine President Volodymyr Zelenskiy on Sunday, said he would be speaking to him again later on Monday or Tuesday morning to make sure they were "on the same page".

The White House said Biden also consulted on Monday with Italian Prime Minister Giorgia Meloni about the situation.

Biden said he and his team would continue assessing the fallout from the incident.

"It's still too early to reach a definitive conclusion about where this is going," he added.

He said his message to allies was "it's important that we stay completely coordinated".

Kirby said the United States does not know the parameters of the deal reached between Putin and Prigozhin that ended the uprising. He said he did not know Prigozhin's whereabouts.

"We're not taking sides in this internal matter," he said.

Kirby said a new package of US assistance for Ukraine would be announced soon. Sources told Reuters that the United States would announce as soon as Tuesday a new military aid package for Ukraine worth up to $500 million.