By Nathan Layne and Sarah N. Lynch

NEWYORK/WASHINGTON (Reuters) – U.S. President Donald Trump’s former campaign manager Paul Manafort breached his plea agreement with Special Counsel Robert Mueller’s office by lying to prosecutors about matters which are material to its Russia probe, a federal judge ruled on Wednesday.

The ruling concludes weeks of wrangling between Manafort’s lawyers and the special counsel over whether he had intentionally lied to prosecutors, impeding their investigation into Russian interference in the 2016 U.S. election and possible collusion between Russia and the Trump campaign.

U.S. District Judge Amy Berman Jackson, who is overseeing the Manafort case in a Washington court, found there was a “preponderance” of evidence that Manafort lied on three different topics, including his communications with his former business partner Konstantin Kilimnik, whom prosecutors say has ties to Russian intelligence. Kilimnik has denied such ties.

Jackson cleared Manafort of allegations that he intentionally lied on two other subjects – Kilimnik’s role in an obstruction of justice charge and statements Manafort made about his contacts with members of the Trump administration.

Nevertheless, the ruling will almost certainly deal a blow to any hopes Manafort had of avoiding an extended term of incarceration. Mueller’s prosecutors are now released from their obligation to support a lighter sentence.

“His sentence has the potential of being very lengthy,” said David Weinstein, a former federal prosecutor in Florida.

The judge found that Manafort lied about his interactions with Kilimnik including about the sharing of polling data on the Trump campaign and their discussions over a “Ukrainian peace plan,” a proposal that envisioned ending U.S. sanctions on Russia – long an important objective of Russian President Vladimir Putin’s government.

A court transcript released last week showed that Mueller’s team believed those lies to be “at the heart” of their investigation into potential collusion, which Trump and Russia have both denied.

In a court filing ahead of Wednesday’s ruling, Manafort’s lawyers repeated their argument that their client never intentionally lied to prosecutors and stressed that he corrected any mistakes once they were pointed out to him.

(Reporting by Sarah N. Lynch and Nathan Layne; editing by Tom Brown and G Crosse)