ROUGH CUT (NO REPORTER NARRATION) U.S. President Donald Trump's former campaign chairman Paul Manafort will cooperate with Special Counsel Robert Mueller's probe of Russian election meddling as part of a plea deal, prosecutors told a federal court in Washington on Friday.

Manafort, 69, also pleaded guilty to two criminal counts, becoming the most prominent former Trump campaign official to plead guilty in Mueller's investigation.

In a statement, the White House distanced Trump from the veteran Republican operative who helped get him elected against the odds in 2016.

"This had absolutely nothing to do with the president or his victorious 2016 presidential campaign," White House spokeswoman Sarah Sanders said of the Manafort news on Friday.

"It is totally unrelated." The probe has cast a shadow over the Republican's presidency.

Manafort's decision to cooperate deals a political setback to Trump ahead of congressional elections on Nov.

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Manafort made millions of dollars working for pro-Russian Ukrainian politicians before taking an unpaid position with Trump's campaign for five months.

He led the campaign in mid-2016 when Trump was selected as the Republican presidential nominee at the party convention.

Moscow has denied interfering in the 2016 election and Trump has said there was no collusion.

Manafort on Friday pleaded guilty to one count of conspiracy against the United States and one count of conspiracy to obstruct justice brought by Mueller's team.

Other counts were dropped.