System set up outside Iran’s borders conducted tens of billions in banned trade, according to documents, intelligence officials WASHINGTON—Iran established a clandestine banking and finance system to handle tens of billions of dollars in annual trade banned under U.S.-led sanctions, enabling Tehran to endure the economic siege and giving it leverage in multilateral nuclear talks, according to Western diplomats, intelligence officials and documents. The system, which comprises accounts in foreign commercial banks, proxy companies registered outside the country, firms that coordinate the banned trade, and a transaction clearinghouse within Iran, has helped Tehran resist the Biden administration’s pressure to rejoin...