It's a case that has captivated Turkey and rattled Ankara: Reza Zarrab has become the star witness in a New York trial over alleged subversion of US economic sanctions against Iran, implicating a former Turkish minister and President Recep Tayyip Erdogan.

The Turkish-Iranian gold trader -- who was arrested in March 2016 en route to a family trip to Miami -- this week revealed in Manhattan federal court that he paid more than 50 million euros in bribes to former Turkish economy minister Zafer Caglayan between 2012 and 2013.

This allowed him to become a key intermediary of a complex but lucrative regional trade circuit that enabled Iran, via the Turkish public banking institution Halkbank, to inject billions of euros of hydrocarbon revenues into the international banking sector, all the while circumventing US sanctions prohibiting trade with Tehran.