Cohen made a surprise appearance Thursday in a New York courtroom at around 9 a.m.
He admitted to making false statements in 2017 to the U.S. Senate Select Committee on Intelligence about a plan to build a Trump Tower in Moscow.
In August, Cohen pleaded guilty to other federal charges involving his taxi businesses, bank fraud and his campaign work for Trump.
The court appearance is ongoing.
One of the prosecutors working with Special Counsel Robert Mueller was present in the courtroom.
Cohen's lawyer told the judge the plea deal involved cooperation with Mueller's investigation of Russian interference in the U.S. election.
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