For three weeks, a Turkish banker, Mehmet Hakan Atilla, has been on trial in Manhattan, charged with participating in a billion-dollar scheme to smuggle oil for gold in violation of United States sanctions on Iran.

But on Friday, the case took an unusual turn when the judge, Richard M. Berman of Federal District Court, sharply criticized Mr. Atilla’s lawyers for injecting a longstanding Turkish political dispute into the case.

“The defense,” the judge said, “appears quite willing to join a rather far-fetched conspiracy theory bandwagon, which has been constructed and developed far outside any United States courtroom.”

Judge Berman was alluding in part to Turkish officials’ harsh attacks on the United States prosecution of Mr. Atilla and a former co-defendant, Reza Zarrab, a Turkish-Iranian businessman who has pleaded guilty and testified against Mr. Atilla.