"The same is true with regard to the Government's allegation that Mr. Manafort lied about sharing polling data with Mr. Kilimnik related to the 2016 presidential campaign", they wrote.
Although the filing does not say whether the polling information was public or what was done with it, it raises the possibility that Russian Federation might have used inside information from Mr Trump's Republican campaign as part of its effort to interfere with the election on Mr Trump's behalf.
The filing did not provide further details on the Madrid meeting or the peace plan, although Mueller has scrutinized a proposal by a Ukrainian lawmaker that involved, among other outcomes, the lifting of USA sanctions on Russian Federation, according to people familiar with the matter. At around the same time, Russian government operatives were allegedly hacking Democratic computers to help Trump and orchestrating a social media propaganda scheme to sway voters against Trump's electoral opponents.
Manafort joined Trump's presidential campaign in March 2016 and became his campaign chairman in May. Tuesday's revelation demonstrates that a member of the Trump campaign was having conversations with a Russian about Ukraine while the campaign was ongoing. Trump has said there was no collusion between his campaign and Moscow.
Jackson had said she expected she would be required by each side to assess Manafort's truthfulness at sentencing, and gave prosecutors a week to respond to Tuesday's filing by and set a hearing for arguments January 25. Manafort has not been charged with crimes related to his work for Trump.
A jury in Alexandria, Va., convicted Manafort on charges of bank and tax fraud in August, after which he agreed to plead guilty to two separate charges and cooperate with Mueller's investigation. Kilimnik had spent a decade working as a translator and fixer for Manafort's political consulting business in Ukraine.
Parts of a court filing that were meant to be redacted by Manafort's legal team, were released publicly on Tuesday, CNN reported.
What does the filing say?
The special counsel's office declined to comment Tuesday.
Manafort's attorneys insisted in the filing that the exchange did not constitute "outreach" to the president. Manafort had told investigators he had no direct or indirect contact with White House officials since Trump's inauguration, but Manafort had been in touch with officials as recently as the spring, according to the special counsel's assertions.
Days before his second trial in a DC federal court was set to begin, Manafort flipped - admitting he masterminded an illegal scheme to lobby for Ukrainians and launder the revenue. If he is found to have breached the deal, he would lose any sentencing credits for acceptance of responsibility, prosecutors said. It was during some of these nine sessions, in September and October, that prosecutors believe he lied to them. Manafort's attorney disputes the allegation saying he "provided complete and truthful information to the best of his ability".
U.S. District Judge Amy Berman Jackson had given Manafort's lawyers until Monday to make a decision. A public hearing is scheduled on that question for later this month. He was also accused of lying about his interactions with Kilimnik and another unspecified Justice Department investigation.