The assets of gold trader Reza Zarrab and his close relatives will be confiscated over espionage charges as part of the ongoing probe launched by the Istanbul Public Prosecutor's Office.

Zarrab was arrested in Miami in March 2016 upon his entry in the U.S. for allegedly evading a U.S.-imposed sanction on Iran, lifted three months before his arrest, with multiple money transfers.

Officials in Turkey have argued that the case has been turned into a political move against Ankara.

Turkey's claims were proved after the judge overseeing the Zarrab case was linked to the Gülenist Terror Group (FETÖ), led by fugitive preacher Fetullah Gülen, who has lived in a self-imposed exile in Pennsylvania since 1999.

The Turkish government has accused the group of exploiting the case by illegally obtaining and fabricating evidence, including wiretap records done by now-sacked FETÖ-linked police officers.

Ankara says the so-called "evidence" was illegal for a court to use under U.S. law, which requires that any piece of evidence must be obtained through legal means.

Zarrab has pleaded guilty and testified as the prosecution's key witness at the U.S. trial of a banker on charges the two of them violated economic sanctions against Iran, ending weeks of speculation in a case that has strained relations between the U.S. and Turkey.