Turkish authorities on Saturday opened an investigation into two U.S. prosecutors involved in a case against a Turkish-Iranian businessman. Preet Bharara, the former U.S. attorney for the Southern District of New York, and his successor, Acting U.S. Attorney Joon H. Kim, were named by the Istanbul prosecutor's office as the focus of the probe, according to Turkey's official Anadolu news agency. Turkish prosecutors say the sources of documents and wiretaps used as evidence in the U.S. case against gold trader Reza Zarrab are unknown and constitute a violation of international law. Zarrab was arrested last year and faces charges for allegedly conspiring to help Iran evade sanctions. A former Turkish economy minister and the head of a state-owned bank also stand accused in the case. Turkish authorities have painted the case as politically motivated and accused Bharara of having ties to Pennsylvania-based cleric Fethullah Gulen, who Istanbul claims masterminded a failed coup in 2016.