Washington (CNN) George Aref Nader, who was a key witness in special counsel Robert Mueller's Russia investigation, was arrested on child pornography charges Monday in New York, federal prosecutors announced Monday.

Nader was arrested upon arrival at John F. Kennedy International Airport for "transporting visual depictions of minors engaged in sexually explicit conduct."

He previously pleaded guilty to the same charge in 1991, the Justice Department said.

If convicted, he faces a minimum sentence of 15 years in prison and a maximum of 40 years.

Nader was charged by prosecutors in Virginia, but made his initial appearance before a magistrate judge in Brooklyn on Monday. US Magistrate Judge Cheryl Pollack postponed a decision on Nader's bail until Tuesday in order to give Nader's attorney additional time to provide details of a proposed security arrangement that can accommodate what the attorney said is his client's serious medical condition.

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