ANKARA (Reuters) - Turkey s justice minister has told his U.S. counterpart that a former Turkish police investigator who testified at the trial of a Turkish banker in New York this week is wanted by Ankara and should be swiftly returned, ministry sources said on Friday. Huseyin Korkmaz gave evidence at the New York trial of a Turkish banker who is charged with helping Iran evade U.S. sanctions, in a case which has strained ties between NATO allies Turkey and the United States.  It has been requested by our judicial offices that (Korkmaz) be temporarily arrested with the aim of being repatriated, based on alleged crimes,  Justice Minister Abdulhamit Gul said in a letter to U.S. Justice Secretary Jeff Sessions, according to the sources at his ministry.  We expect that the request is met on positive terms and the previously mentioned person be repatriated as soon as possible.  The Turkish government has said followers of U.S.-based cleric Fethullah Gulen, who it blames for last year s failed military coup, are behind the case brought in the United States. Gulen has denied any role in the coup attempt.  I want to point out that a fugitive, a terror suspect facing serious allegations, taking part in this case in your country as a witness is big enough a scandal,  Gul said, adding that the case could cause irreparable damage to relations if action was not taken. Korkmaz told the trial at Manhattan federal court this week that he feared he would be tortured if he returned to Turkey, where he led an investigation involving Turkish officials and Mehmet Hakan Atilla, the bank executive on trial in New York. Gul s letter repeated Turkish allegations of contact between members of the judiciary who have handled the case and members of the Gulen network.  Foreign Minister Mevlut Cavusoglu has said the cases showed the extent to which Gulen had infiltrated American state institutions, including its judiciary.  Needless to say, those claims are ridiculous,  Acting U.S. Attorney, Kim H. Joon said last month in response to such accusations.  The case has been handled by career prosecutors concerned only with U.S. law, not Turkish politics, Kim said, adding:  They re not Gulenists.  Prosecutors have accused Atilla, an executive at Turkey s state-owned Halkbank, of working with Turkish-Iranian gold trader Reza Zarrab and others to help Iran evade U.S. sanctions through fraudulent gold and food transactions. Atilla, 47, has pleaded not guilty. Zarrab, 34, pleaded guilty and testified for U.S. prosecutors. Turkish President Tayyip Erdogan, who has governed Turkey for almost 15 years, has dismissed the case as a politically inspired attempt to bring down the Turkish government. 