George Nader was indicted Friday on charges of transporting a 14-year-old boy for sexual activity. (AP)

A Trump associate and key witness in former special counsel Robert S. Mueller III’s investigation of Russian election interference has been indicted on charges of transporting a 14-year-old boy for sexual activity.

George Nader pleaded not guilty in Alexandria federal court on Friday; a trial is set for Sept. 30. Judge Leonie M. Brinkema declined to let him out on bail, citing “the nature of the charges and [his] extensive overseas connections.”

According to the three-count indictment, in February 2000 Nader brought a 14-year-old boy from Europe to the United States through Dulles International Airport and brought him to his home in Washington for sexual activity.

In court, Assistant U.S. Attorney Jay Prabhu indicated that a witness in the case from the Czech Republic may testify at trial.

Nader, 60, was arrested last month at John F. Kennedy International Airport in New York. In initial charges filed against him, authorities alleged he had carried child pornography when he arrived in the country from Dubai in January 2018.

Attorneys for Nader declined to comment. But in a motion for bond, they argued that the charges were overblown based largely on videos sent to Nader.

“None of the text messages surrounding the videos at issue (all but two of which were allegedly sent to the iPhone in question) indicate that Mr. Nader in any way solicited this content,” they wrote. The new charge of transporting a minor, the defense attorneys say, is “factually unfounded” and outside the statute of limitations, which was eliminated for child sex crimes in 2006.

The explicit videos of minors were found on one of the phones Nader gave to FBI agents working for the special counsel. He came and went from the country several times while being interviewed by Mueller’s team about his contacts with Trump’s associates. But by the time he was charged under seal by prosecutors in Alexandria last April, he had left the country and did not return until more than a year later, for treatment following heart surgery.

Nader is arguing that he should be released for further rehabilitation and physical therapy. Brinkema said she would consider the motion but indicated concern that his “incentive to flee is quite high.”

A well-connected adviser to the United Arab Emirates, Nader was seen by Trump allies as an helpful operator for navigating politics in the Middle East. He attracted Mueller’s interest for helping arrange a meeting in the Seychelles in January 2017 between Erik Prince, a Trump supporter who founded the private security firm Blackwater, and a Russian official close to Russian President Vladi­mir Putin.

Nader later visited the White House several times, meeting with senior adviser Stephen K. Bannon and Jared Kushner, the president’s son-in-law and senior adviser, according to people familiar with his visits.

He was born in Lebanon and came to the United States as a teen; Nader later founded a magazine on Middle East affairs that put him in contact with leaders across the region.

When he was convicted 28 years ago of transporting child pornography, he received a reduced sentence after influential figures argued privately to the court that he helped free U.S. hostages then held in Lebanon.

Throughout his prominent career he has repeatedly been investigated for offenses related to underage boys.

In 1985, he was indicted by a federal grand jury in Washington on two counts of mailing and importing child pornography. Those charges were dismissed after Nader’s lawyers successfully argued that authorities had illegally seized evidence in the case.

Twice in 1988, Nader received sexually explicit material via a post office box in Cleveland, according to court filings, but he was not charged until 1990, when he was caught at Dulles with explicit videos of young boys. He served about six months in federal custody in a facility on work release, court records show.

In 2003, Nader was convicted in the Czech Republic of what his attorney Christopher Clark described in court as “contributing to the moral corruption of society” after “having a relationship with two young men two years under the age of consent.”