Washington (CNN) Former Trump campaign chairman Paul Manafort has agreed to cooperate with the Justice Department, including in special counsel Robert Mueller's investigation of Russian interference in the 2016 presidential election.

Manafort pleaded guilty to one count of conspiracy against the US and one count of conspiracy to obstruct justice due to attempts to tamper with witnesses, according to a court filing Friday.

Prosecutor Andrew Weissmann told the judge Manafort's plea agreement is a "cooperation agreement," and other charges will be dropped at sentencing at "or at the agreement of successful cooperation."

Manafort had proffered information to the government already, Weissmann said in a federal court in a Washington, DC.

The scope of the cooperation was not immediately clear. While President Donald Trump is not mentioned in Friday's filing, nor is Manafort's role in his campaign, the news of the cooperation comes as the President continued to lambast the Mueller investigation on Twitter this week.