31 CFR § 515.201
All of the following transactions are prohibited, except as specifically authorized by the Secretary of the Treasury (or any person, agency, or instrumentality designated by him) by means of regulations, rulings, instructions, licenses, or otherwise, if either such transactions are by, or on behalf of, or pursuant to the direction of a foreign country designated under this part, or any national thereof, or such transactions involve property in which a foreign country designated under this part, or any national thereof, has at any time on or since the effective date of this section had any interest of any nature whatsoever, direct or indirect:
(1) All transfers of credit and all payments between, by, through, or to any banking institution or banking institutions wheresoever located, with respect to any property subject to the jurisdiction of the United States or by any person (including a banking institution) subject to the jurisdiction of the United States;
(2) All transactions in foreign exchange by any person within the United States; and
(3) The exportation or withdrawal from the United States of gold or silver coin or bullion, currency or securities, or the earmarking of any such property, by any person within the United States.