Iran has conducted “billions of dollars” annually in trade despite United States ‘maximum pressure’ sanctions, the Wall Street Journal reported Friday.

The Journal offered details on how Iran has sold oil and other commodities, citing information from unnamed “Western” diplomats and intelligence officials. The Journal also reviewed financial transactions of several hundred million dollars for proxy Iranian companies in 61 accounts at 28 banks in China, Hong Kong, Singapore, Turkey, and the United Arab Emirates.

Although there is a clearing system inside Iran and exporters ‘trade’ foreign currency on ledgers, hard cash is also withdrawn from foreign accounts and taken by couriers to Iran. The Journal said “much of the revenue” was still in bank accounts outside the country.

As usual with sanctions, such an informal infrastructure has been open to corruption as came to light during the administration of President Mahmoud Ahmadinejad (2005-13). Among those convicted in Iran over malpractice, businessman Babak Zanjani is in jail facing the death penalty after reportedly netting $2.7 billion acting as a middleman selling oil during international sanctions in the early 2010s.

One Western official cited by the Journal called Tehran’s reaction to maximum pressure sanctions – which threaten punitive action against anyone dealing with Iran’s financial system and which sent the country into two years’ deep recession – “an unprecedented governmental money-laundering operation.”