Washington (CNN) Robert Mueller's special counsel's office hit former Trump campaign chairman Paul Manafort with two more criminal charges Friday and added his longtime business associate Konstantin Kilimnik as a second defendant in the case, after accusing them earlier in the week of attempting to convince witnesses to commit perjury.

The expanded criminal allegations ratchet up the pressure Manafort faces to cut a deal with the special counsel's office as he awaits two criminal trials. If he is found guilty in both cases, 69-year-old Manafort could be sent to prison for the rest of his life.

The case now accuses both Manafort and Kilimnik, 48, of Moscow, of obstruction of justice and conspiracy to obstruct justice, meaning they allegedly worked together to contact two possible witnesses in Manafort's case since February.

Prosecutors already claimed that Manafort misled federal authorities for years about his lobbying work in the US for Ukrainian politicians before he joined the Trump campaign. He has pleaded not guilty to the charges. He is also fighting a handful of financial crime charges, including bank fraud, against him in Virginia federal court.

Kilimnik has long been a close business colleague of Manafort's that prosecutors have said in previous filings has ties to Russian intelligence.

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