Former New York mayor and prominent Donald Trump supporter Rudolph Giuliani traveled to to meet with Turkish president Recep Tayyip Erdogan on behalf of his client Reza Zarrab—a Turkish gold trader jailed on federal charges of conspiring to violate U.S. sanctions on Iran, the New York Times reports.

The United States attorney’s office in Manhattan said Giuliani and another prominent lawyer, Michael B. Mukasey, “have been retained by the defendant and are involved in, and will continue to be involved in, efforts to explore a potential disposition of the criminal charges in this matter.”

According to the Times, prosecutors contend Zarrab—who holds dual citizenship in Iran and Turkey—helped facilitate “millions of dollars in illicit transactions” in an effort to bypass U.S. sanctions on Iran and “allegedly tricked numerous U.S. financial institutions into processing barred transactions.”

Zarrab’s detention has been publicly criticized by president Erdogan.

Last year, a judge denied a motion to dismiss charges against Zarrab at the bequest of Preet Bharara, the former United States attorney for the Southern District of New York who was fired by Trump earlier this month.

Read the full story at the New York Times.