Special counsel Robert MuellerRobert Swan MuellerSasse: US should applaud choice of Mueller to lead Russia probe MORE said in a court filing on Monday that President TrumpDonald John TrumpSunday shows preview: Trump sells U.N. reorganizing and Kavanaugh allegations dominate Ex-Trump staffer out at CNN amid “false and defamatory accusations” Democrats opposed to Pelosi lack challenger to topple her MORE's former campaign chairman Paul ManafortPaul John ManafortDem warns Trump: 'Obstruction of justice' to fire Rosenstein Ex-White House official revises statement to Mueller after Flynn guilty plea: report Former White House lawyer sought to pay Manafort, Gates legal fees: report MORE has attempted to tamper with potential witnesses while on pretrial release. 

Mueller's team has asked the court to revoke or revise Manafort's release conditions, including his bond and house arrest, in the wake of the filing, which was first reported by Reuters.

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FBI agent Brock Domin said in the filing that Manafort and a longtime associate linked to Russian intelligence attempted to contact via phone call, text and encrypted messages two people from the "Hapsburg group," which Manafort had worked with to lobby for Ukrainian interests. 

Domin said that Manfort's attempts at contact were “in an effort to influence their testimony and to otherwise conceal evidence” and that the probe into the matter was still ongoing. 

Domin said he believed the effort was an attempt to "suborn perjury."

In a Tuesday statement, Manafort's representation said the filing would not alter his defense.

"Mr. Manafort is innocent and nothing about this latest allegation changes our defense. We will do our talking in court," his attorneys said.

Mueller's investigation into Moscow's meddling in the 2016 presidential election and any possible coordination with the Trump campaign reached its anniversary last month.

The special counsel's office hit Manafort with a 12-count indictment last year, which included conspiracy against the United States, tax fraud and money laundering. 

Manafort has pleaded not guilty to the charges, which are not directly related to his work for the Trump campaign. 

His former business associate, Richard Gates, pleaded guilty to one count of conspiracy against the United States and one count of making a false statement to the FBI agents investigating Russian interference earlier this year as part of a plea deal with Mueller's team. 

Former national security adviser Michael Flynn, former Trump campaign adviser George PapadopoulosGeorge Demetrios PapadopoulosFlynn sentencing move spurs questions about duration of Mueller probe Time for sunshine on Trump-Russia investigation Trump to declassify controversial text messages, documents related to Russia probe MORE and Dutch attorney Alex van der Zwaan have all also pleaded guilty in the case. 

A grand jury also indicted 13 Russian nationals and three Russian entities earlier this year for allegedly meddling in the 2016 presidential election. 

Manafort's former son-in-law, who is reportedly intimately familiar with his business dealings, also reached a plea deal with federal prosecutors last month.

Trump has spoken out about Manafort in recent days, slamming the FBI and Department of Justice for not telling him that agents were “secretly investigating" Manafort during the 2016 presidential race. 

Trump sought to distance himself from Manafort in a subsequent tweet, saying that Manafort was only with the campaign for a short period of time. 

—Updated Tuesday at 1:01 p.m.