Washington(CNN) Special counsel Robert Mueller believes that Paul Manafort was sharing polling data and discussing Russian-Ukrainian policy with his close Russian-intelligence-linked associate, Konstantin Kilimnik, while he led the Trump presidential campaign, according to parts of a court filing that were meant to be redacted by Manafort's legal team Tuesday but were released publicly.

Manafort discussed a Ukrainian peace plan with Kilimnik, his lawyers acknowledged. He also shared polling data related to the 2016 presidential campaign with Kilimnik, Manafort's legal team acknowledges in their court filing.

The details accidentally released Tuesday are the closest public assertion yet in the Mueller cases of coordination between a Trump campaign official and the Russian government, as Kilimnik is believed to be linked to Russian military intelligence. It's a major acknowledgment from the Mueller team that their investigation into Russian interference in the 2016 election is finding potential contact between at least one Trump campaign official and the Kremlin.

The Ukraine peace plan that they discussed likely would have dealt with Russian intervention in the region. 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.

Kilimnik has long been suspected to be central to Mueller's investigation into Russian influence in the 2016 presidential election. The revelations in the court filing Tuesday seem to confirm that.

Manafort's filing also acknowledges he met with Kilimnik in Madrid. Later Tuesday, Manafort spokesman Jason Maloni said that meeting was in January or February 2017, after Trump was elected. There are two known meetings during the campaign between Manafort and Kilimnik.

The sentences revealed in the filing certify for the first time Mueller's interest in Kilimnik's political actions during the campaign. Manafort has not been charged with crimes related to his work for Trump. Kilimnik only faces a charge from Mueller related to allegedly helping Manafort tamper with witnesses following his arrest.

Kilimnik has not entered a plea in US courts, and Manafort has pleaded guilty to the witness tampering allegation and has been convicted on several lobbying-related financial crimes.

Prosecutors have previously said they believe Kilimnik has ties to the military intelligence unit the GRU, which allegedly hacked the Democratic Party and leaked damaging emails while Manafort ran Trump's campaign operation. Manafort and Kilimnik have been close colleagues for years.

The errant admissions in Manafort's court filing also acknowledge that a person wanted to use his name when meeting President Donald Trump.

Errant redactions

The revelations come in Manafort's written response to accusations that Manafort lied to Mueller's team during cooperation interviews. Those portions had been redacted given Mueller's sensitivities toward ongoing investigations, Manafort's lawyers said, but the redactions were able to be read in the document filed with the federal court online.

Manafort says he did not intentionally mislead Mueller. His legal team offered explanations of human nature as the reasons for his misstatements. He also tried to help the investigation in several ways, such as by handing over his computers, email accounts and passwords to Mueller, he says in a new filing.

Previously, the special counsel's office outlined five areas in which they believe Manafort lied, including about his contact with Kilimnik, who is of interest to the Mueller investigation, and about his communication with White House officials as recently as last year, but redacted some details of what they know and how they know it.

Mueller's accusation that Manafort lied already pulled into question the former campaign chairman's possibility for leniency in the justice system and his usefulness to federal authorities -- though it raised the possibility President Donald Trump could see Manafort as an ally and offer him a pardon.

The special counsel's office declined to comment Tuesday.

Manafort's attorneys did not respond to a request for comment Tuesday about the filing error, though they corrected it in the court's official record.

Manafort's situation

Manafort has been in jail since June, after prosecutors accused him of attempting to sway witness' testimony against him while he was under house arrest. Manafort was convicted by a jury in a Virginia federal court for eight tax and bank fraud charges. He will be sentenced for those crimes in early February.

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. In return, prosecutors said they would consider asking the judge for leniency at his eventual sentencing.

The plea deal instantly turned him into the person whom many believed would be the Mueller investigation's star cooperator.

As part of his guilty plea, Manafort agreed to sit for interviews with investigators. It was during some of these nine sessions, in September and October, that prosecutors believe he lied to them.

Manafort initially indicated that he would push back on the investigators' lying accusation, because he believed he had given them truthful information during cooperation.

The judge in DC federal court who has overseen his case, Amy Berman Jackson, gave him the opportunity to respond before she would hold a hearing about the facts of the situation.

That hearing is currently scheduled for later this month. Jackson is set to sentence Manafort for conspiracy and witness tampering charges in March.

For the two charges he currently faces in DC federal court, Manafort could receive 17 to 22 years in prison, his plea agreement says.

He has been wheelchair bound for months, his lawyers say, because of gout, and has been kept essentially in solitary confinement for his own safety.