It also included an allegation that a fixer described by the Federal Bureau of Investigation as a former Russian spy, Konstantin Kilimnik, helped Manafort obstruct justice.
In a response to the accusations made earlier in the week, Manafort's attorneys argued in a filing late Friday night that the special counsel allegations of witness tampering "conjures a sinister plot" to persuade associates to perjure themselves, but disputes that the evidence provided establishes any tampering.
Prosecutors complained to a federal judge earlier this week that Manafort - and, apparently, Kilimnik - had been contacting people who knew about that work to ask them to tell jurors that the Ukraine lobbying had only taken place inside Europe.
Paul Manafort, President Donald Trump's former campaign chairman, has pleaded not guilty to a variety of charges brought by Special Counsel Robert Mueller's team.
The indictment, filed by Mueller in District of Columbia federal court, included new counts against Trump's former campaign chair Paul Manafort and the operative, Manafort aide Konstantin Kilimnik, for tampering with witnesses about their lobbying for Ukraine.
The latest charges increase Manafort's legal jeopardy if he continues a battle with prosecutors. The spokesman, Jason Maloni, said Friday that Manafort and his lawyers were reviewing the new charges.
Kilimnik has always been a close business colleague of Manafort's that prosecutors have said in previous filings has ties to Russian intelligence. He has pleaded not guilty to all counts, and is expected to go on trial in Washington, D.C., on September 17.
Manafort and Kilimnik's allegedly criminal contact with the two witnesses who once worked with them doing public relations began on a day, February 23, when Manafort's case became far tougher to overcome.
Kilimnik has also drawn the scrutiny of congressional committees investigating Russian interference in the 2016 presidential campaign. The indictment marked the first charges for Manafort's associate, Konstantin Kilimnik, who is believed to be in Moscow and probably safe from arrest because Russian Federation does not extradite its citizens.
Prosecutors say that the "P" in the message refers to Manafort and that the assertions in the texts are untrue.
According to court filings, after Manafort was accused in February of additional instances of secretly lobbying on behalf of a foreign government without registering as a lobbyist, he and Kilimnik repeatedly contacted the two executives to emphasize that their past work together did not involve American officials and therefore did not constitute lobbying in the United States.
In the summer of 2016, Manafort emailed Kilimnik and told him to offer private briefings on the US presidential campaign to Deripaska in an effort to resolve the dispute, people close to the situation have said.
The new charges will factor heavily into whether U.S. District Judge Amy Berman Jackson allows Manafort to remain on house arrest. The charges stemmed from his PR and campaign work for former pro-Russian Ukrainian president Viktor Yanukovych. "Closer scrutiny of this 'evidence" reveals that the Special Counsel's allegations are without merit because Mr. Manafort's limited communications can not be fairly read, either factually or legally, to reflect an intent to corruptly influence a trial witness". Prosecutors named him in one count of obstruction of justice, and one count of conspiracy to obstruct justice.
He was described as the intermediary through which Manafort volunteered to brief his onetime client, aluminum tycoon Oleg Deripaska, about the Trump campaign.
In Friday's indictment, Mueller accused Kilimnik of taking part in the covert lobbying scheme, and in trying to influence potential witnesses.