The former son-in-law of Paul Manafort, the one-time chairman of President Donald Trump's campaign, has cut a plea deal with the Justice Department that requires him to cooperate with other criminal probes, two people with knowledge of the matter said.

The guilty plea agreement, which is under seal and has not been previously reported, could add to the legal pressure on Manafort, who is facing two indictments brought by Special Counsel Robert Mueller in his probe of alleged Russian meddling in the 2016 presidential election.

Manafort has been indicted in federal courts in Washington and Virginia with charges ranging from tax evasion to bank fraud and has pleaded not guilty to the charges.

Jeffrey Yohai, a former business partner of Manafort, was divorced from Manafort's daughter last August.

Yohai has not been specifically told how he will be called on to cooperate as part of his plea agreement, but the two people familiar with the matter say they consider it a possibility that he will be asked to assist with Mueller's prosecution of Manafort.

Legal experts have said that Mueller wants to keep applying pressure on Manafort to plead guilty and assist prosecutors with their probe. Manafort chaired the Trump campaign for three months before resigning in August 2016.