WASHINGTON, June 25 (Reuters) - The unprecedented challenge to Russian President Vladimir Putin by Wagner fighters has exposed fresh "cracks" in the strength of his leadership that may take weeks or months to play out, U.S. Secretary of State Antony Blinken said on Sunday.

Blinken and members of the U.S. Congress said in a series of television interviews that Saturday's turmoil in Russia has weakened Putin in ways that could aid Ukraine's counteroffensive against Russian forces within its territory while benefiting Russia's neighbors, including Poland and the Baltic states.

"I don't think we've seen the final act," Blinken said on ABC's "This Week" program after an aborted mutiny by forces led by Yevgeny Prigozhin.

Blinken said tensions that sparked the action had been growing for months and added the threat of internal turmoil could affect Moscow's military capabilities in Ukraine.

"We've seen more cracks emerge in the Russian facade. It is too soon to tell exactly where they go, and when they get there. But certainly, we have all sorts of new questions that Putin is going to have to address in the weeks and months ahead," Blinken told NBC's "Meet the Press" program.

Blinken described the turmoil as an "internal matter" for Putin.

"Our focus is resolutely and relentlessly on Ukraine, making sure that it has what it needs to defend itself and to take back territory that Russia seized," Blinken said.

U.S. officials expect to learn more soon about the events that unfolded in Russia, including details of the deal with Prigozhin mediated by Belarusian President Alexander Lukashenko that led Wagner fighters to return to their bases.

"It may be that Putin didn't want to debase himself to the level of negotiating directly with Prigozhin," Blinken said.