U.S. prosecutors have charged several former top aides to Turkish President Recep Tayyip Erdogan with involvement in a conspiracy to secretly help Iran evade U.S. sanctions.

In an indictment filed in the U.S. District Court in Manhattan on September 6, former Turkish Economic Minister Mehmet Zafer Caglayan was charged with taking tens of millions of dollars in bribes in cash and jewelry to assist and cover up a scheme to help Iran process transactions through the U.S. financial system in violation of sanctions law.

The indictment expands on the government's case against a wealthy Turkish-Iranian businessman, Reza Zarrab, who was arrested last year and faces trial in New York on charges of helping Iran evade sanctions by supplying Tehran's government and other Iranian entities with currency and gold.

Prosecutors had said they would show that the case involved people at "high levels" in both Turkey and Iran. Zarrab's lawyers have sought to secure a political and diplomatic settlement of the case, with Erdogan making a personal appeal on Zarrab's behalf on a recent visit to the White House.

Also named in the latest indictment was Suleyman Aslan, the general manager of a Turkish government-owned bank owned, as well as his deputies Levant Balkan and and Mehmet Hakan Atilla. They were also charged with taking bribes and using the bank to facilitate and hide Zarrab's transactions on behalf of Iran. Several of Zarrab's employees and associates also have been charged.

Zarrab and Atilla are in custody in New York, with their trial scheduled to begin on October 30. The other Turkish officials named in the indictment remain at large, prosecutors said.