The Bush administration has decided to impose sanctions on Chinese, Armenian and Moldovan companies accused of aiding Tehran's alleged weapons programmes.
He told reporters the US Congress would be formally notified soon of the decision, which is being taken under the 2000 Iran Nonproliferation Act.
The sanctions are imposed because of "weapons transactions with Iran" - part of what President Bush calls the "axis of evil" along with Iraq and North Korea - and to demonstrate that America is paying increased attention to the Iran Nonproliferation Act, the official said.
He did not give names or numbers of the companies affected nor the exact nature of their activities.
The official said the companies and individuals in Moldova and Armenia may be a "front" for Russian entities, given those countries' status as former Soviet republics.
Since the September 11th attacks on the United States, the administration has vowed to crack down on states developing nuclear, chemical, biological and missile technology that could be used by terrorists.