KYIV -- Konstantin Kilimnik, the alleged Russian intelligence operative who helped run Paul Manafort's operations in Kyiv for roughly a decade, boasted of the duo's closeness to RFE/RL in a 2017 interview. "The only guy who Manafort can conceivably talk to in Ukraine is basically me," he said.

Kilimnik added that, while Manafort was working as Donald Trump's campaign chairman in 2016, he was also "briefing [Manafort] on Ukraine."

On January 15, Special Counsel Robert Mueller's office suggested in a court filing that the two men spoke a lot, before and long after Manafort was criminally charged, and specifically about an initiative to bring peace to Ukraine that was likely very favorable to the Kremlin.

If confirmed, that would indicate that the pair were doing so while Manafort was working for Trump's campaign and Russia was allegedly interfering in the 2016 election to help his candidate win.

The heavily redacted court filing shines the brightest light yet on what Manafort was asked to testify about in two grand jury sessions and lays out "documentary evidence" of Manafort's repeated lies to the grand jury and prosecutors even after he pleaded guilty and began cooperating with Mueller's investigation.

And it provides more details about Manafort's interactions with Kilimnik, his longtime deputy in Kyiv who has emerged as a central figure in Mueller's investigation into Russian interference in the 2016 presidential election. Notably, it indicates that the two communicated about a peace plan for Ukraine during the 2016 presidential campaign and well beyond.

'New Initiative For Peace'

According to the court filing, between August 2, 2016 and March 2018, Manafort and Kilimnik communicated about an issue that is redacted in the filing. An exhibit attached to the filing that shows Manafort had worked on a document titled "New initiative for Peace copy" in February 2018 as part of his ongoing interactions with Kilimnik, suggests the two were collaborating on a plan for the future of Ukraine.

The revelation comes a week after defense lawyers for Manafort accidentally revealed in a court filing that was improperly redacted that Mueller accused him of discussing a "Ukraine peace plan" with Kilimnik "on more than one occasion" after being shown documents by investigators.

In an interview and follow-up conversations with RFE/RL in February 2017, Kilimnik outlined a peace initiative which he called the "Mariupol plan" – a reference to the city in southeastern Ukraine that sits near the front line of the simmering war between Russia-backed separatists and Ukrainian forces and on the Sea of Azov.

The initiative is seemingly separate from the infamous Ukraine peace plan that involved ex-Trump attorney Michael Cohen and former Ukrainian lawmaker Andriy Artemenko, which reached the desk of former national-security adviser Michael Flynn.

Kilimnik's plan -- which he claimed at the time Manafort was not involved with -- recommended bringing disgraced former Ukrainian President Viktor Yanukovych back from exile in Russia to the country that overthrew him in a deadly revolution to be the head of the war-torn eastern regions of Donetsk and Luhansk.

It is unknown whether the "Mariupol plan" and the "New initiative for Peace" are the same.

Regardless, if confirmed that Manafort was working on the "Mariupol plan" outlined by Kilimnik or a similar plan during the time frame outlined by Mueller, it would mean that Manafort was involved in a Ukraine peace plan viewed as advantageous for the Kremlin while Russia was reportedly interfering in the 2016 election to help his candidate win.

Shadowy Operative

In the court filing by Manafort's lawyers last week, Mueller was cited as saying "Manafort 'conceded' that he discussed or may have discussed a Ukraine peace plan with Mr. Kilimnik on more than one occasion," and "acknowledged" that he and "Kilimnik met while they were both in Madrid."

The date of the meeting in the Spanish capital was not disclosed, but a Manafort spokesperson told journalists it happened sometime in January or February 2017.

Kilimnik is a shadowy political operative and a linguist who studied at a university linked to Russia's military intelligence agency, known as the GRU. It, along with the Federal Security Service (FSB), is alleged to have been involved in the Kremlin's effort to interfere in the 2016 U.S. presidential election.

Unlike Manafort -- who was convicted in August by a federal court in Virginia of bank fraud and tax evasion connected to his work in Ukraine and later pleaded guilty in a separate case to two counts of conspiracy in order to avoid a second trial -- Kilimnik is unlikely to appear in a U.S. courthouse to face charges of obstruction of justice and conspiracy to obstruct justice related to his dealings with Manafort.

The Ukrainian-born Kilimnik, 48, is now believed by Mueller's team to be in Russia. He previously told RFE/RL that he split his time between Kyiv and Moscow, where he reportedly owns a home in a gated neighborhood.

He did not respond to requests for comment for this story.

But during two face-to-face meetings in Kyiv, several phone calls, and many more text messages in 2017 and 2018, Kilimnik insisted to RFE/RL that he did not work for the GRU and said he did not fear Mueller's probe.

In a text message sent on June 20, 2017, he wrote: "No one [from Mueller's team or U.S. law enforcement] has contacted me and probably never will."

Signing off, he quipped, "Well, off to collect my soviet intelligence veteran pension. ;)))"

Also included in the January 15 filing were allegations from Mueller's team that Manafort lied when he said he had not communicated with members of Trump's administration after the president's inauguration.

According to the filing, on May 28, 2018, Manafort received a text message from an associate claiming to have an upcoming meeting with Trump who asked, "If I see [the president of the United States] one on one next week am I ok to remind him of our relationship?" Manafort replied: "Yes…even if not one on one."

Finally, the filing claims that while Manafort turned over electronic devices and digital media to prosecutors, he "did not provide passwords" to officials on more than 10 occasions.