"Today's announcement underscores the success of our sanctions implementation," she said in a statement. "By reducing Iran's oil sales, we are sending a decisive message to Iran's leaders: until they take concrete actions to satisfy the concerns of the international community, they will continue to face increasing isolation and pressure." 

The U.S. sanctions target foreign financial institutions that do business with Iran's central bank by barring them from opening or maintaining correspondent operations in the United States. They would apply to foreign central banks only for transactions that involve the sale or purchase of petroleum or petroleum products.