ISTANBUL (Reuters) - An Istanbul prosecutor has issued arrest warrants for the parents of a former police investigator who gave evidence at the trial of a Turkish banker in the United States last week, the Hurriyet newspaper reported on Wednesday. Turkey has called for the arrest of Huseyin Korkmaz after he testified at the trial of Mehmet Hakan Atilla, a former executive of state-lender Halkbank who is accused of helping Iran evade U.S. sanctions. The Istanbul prosecutor s office was not immediately available for comment. U.S. prosecutors have accused Atilla of working with Turkish-Iranian gold trader Reza Zarrab and others to help Iran evade U.S. sanctions through fraudulent gold and food transactions. The case has strained relations between Turkey and the United States, which are NATO allies. Atilla has pleaded not guilty and Halkbank has denied involvement with any illegal transactions. But Zarrab has pleaded guilty and testified for U.S. prosecutors. Korkmaz said he fled Turkey in 2016 fearing retaliation from the government after leading an investigation in 2013 into Zarrab which implicated high-ranking officials. Hurriyet said the Istanbul prosecutor s order to arrest Korkmaz s parents came after his testimony in the U.S. case in which he said he gave documents related to the 2013 investigation to his mother to keep. Last week, Turkish police summoned a Federal Bureau of Investigation (FBI) official over statements made by Korkmaz in the U.S. court, the state-run Anadolu Agency reported. 