(CNN) George Aref Nader, who was a key witness in special counsel Robert Mueller's Russia investigation, faces new charges of transporting a minor "with intent to engage in criminal sexual activity" and child pornography.

According to a newly unsealed federal indictment in the Eastern District of Virginia, Nader is accused of bringing a 14-year-old boy from Europe to the United States in 2000 for prostitution or sex. Nader engaged in sexual acts with the boy at his Washington, DC, home, the indictment states. Nader also faces two counts of transporting child pornography and "obscene" materials.

He pleaded not guilty to the charges in federal court Friday, according to the Washington Post , and his trial has been set for September 30.

CNN has reached out to Nader's attorneys for comment.

Nader was arrested in June upon his arrival at John F. Kennedy International Airport in New York after being charged under seal with transporting child pornography. He was charged with "transporting visual depictions of minors engaged in sexually explicit conduct."

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