Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

A former cellmate is accusing a Turkish gold trader who is the star prosecution witness in a U.S. sanctions-busting trial of raping him in a federal lockup.

A lawsuit filed late Wednesday in Manhattan Supreme Court alleges that in 2016 and early 2017 Reza Zarrab sexually assaulted a 62-year-old man being held on terrorism support charges at the Metropolitan Correctional Center in lower Manhattan.

Reza Zarrab, seen here in 2013, is accused of raping a cellmate. Ozan Kose / AFP - Getty Images file

"Believing that he was immune from the law and norms of behavior because of his wealth, power and political connections Zarrab at first befriended [the cellmate], gained his confidence, co-opted him and then repeatedly assaulted him," the lawsuit, which was first reported by the New York Times, alleges.

"Zarrab then also threatened and intimidated [the cellmate] thereby delaying [him] from reporting these assaults to the authorities," the suit says.

An attorney for Zarrab, who is in his seventh day of testimony in a high-profile case that has strained U.S.-Turkish relations, said "the allegations are outrageous and false from a source that is not remotely credible."

The U.S. attorney's office in Manhattan declined to comment.

The cellmate's lawyer, Alexei Schacht, told NBC News that the timing of the lawsuit had nothing to do with the sanctions case.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

"I think that he has been complaining about this conduct for some time to different people and he felt like his complaints were not being sufficiently addressed," Schacht said.

Schacht, who is representing the cellmate pro bono in his criminal case, said his bills for the lawsuit were not being paid by a third party. He said there is "absolutely zero chance" the money for his fees was coming from Turkey, where authorities are furious at Zarrab.

Zarrab, a fabulously wealthy and politically connected businessman who is married to a Turkish pop star, was arrested in March 2016 and accused of running a scheme to move billions in Iranian oil and gas money through American banks in violations of U.S. sanctions against Iran.

He was removed from federal lockup after he struck a cooperation agreement with federal prosecutors and agreed to take the stand against Turkish banker Hakan Atilla, who is currently on trial.

But, according to the lawsuit, while Zarrab was still behind bars, he struck up a friendship with a man who was charged with providing material support to the Colombian terrorist organization FARC in the form of weapons procurement and cocaine trafficking.

Zarrab hired a private attorney for the man, sent money to his family in Africa, and arranged to have him moved into his cell, the suit says.

"At about the same time, having given Plaintiff money and other favors, Defendant started telling Plaintiff that he likes having sex with both men and women," the suit claims.

The alleged attacks — one of which involved a cucumber — started in November 2016 and continued until March 2017, according to the cellmate, who pleaded guilty and is awaiting sentencing.

Schacht said that his client did make a formal complaint to the jail about the alleged abuse and there was an investigation. The outcome, he said, was that the Bureau of Prisons could not prove or disprove the accusation. The bureau said it could not comment because of privacy concerns.

The private attorney who represented the cellmate in his terrorism case in 2016 told NBC News his bills were paid by the family, not Zarrab, but he could not say where the family got the money. The public defender who represented him at the time the alleged attacks took place could not be reached for comment.

When Zarrab pleaded guilty to money laundering and fraud charges in October, he also copped to paying a bribe to a federal jail guard for access to alcohol and a cellphone. During cross-examination this week, he revealed the bribe was $45,000 and also conceded he had smoked synthetic marijuana in jail.

The trial has been closely watched from Washington to Ankara because Zarrab has ties to Turkish President Recep Erdogan — and implicated him in the Iranian money scheme. Erdogan's government has since seized Zarrab's assets and rounded up at least 17 of his associates.

Special Counsel Robert Mueller, as part of his investigation into Russian meddling in the election, had been looking into whether Turkish officials tried to bribe Mike Flynn, shortly before he became national security adviser, to make the sanctions case disappear. Flynn's name has not come up during the trial so far.