It is the biggest single action of its kind since the U.S. Congress approved legislation in 2000 aimed at deterring Iranian weapons-of-mass-destruction efforts.

U.S. sanctions are being imposed against a list of 13 companies or businessmen in seven countries. Five are from China. There are two each from Russia and Macedonia, and one each from Belarus, North Korea, Taiwan and the United Arab Emirates.

At a news briefing, State Department spokesman Adam Ereli said the sanctions are being imposed because of "credible information" that the firms have transferred sensitive technology or equipment to Iran.

He said the penalties will last for two years and forbid the affected companies from buying U.S. high-tech equipment or in any way doing business with the U.S. government.

"No department or agency of the U.S. government may procure or enter into any contract for the procurement of any goods, services or technology from these entities," he said. "No department or agency of the U.S. government may provide any assistance to these entities. And new licenses are to be denied and existing licenses suspended for transfers to these entities of items controlled under the Export Administration Act of 1979, or the Export Administration regulations."

The extent of the companies' actual dealings, if any, with the United States are unclear.

Several of the companies named are already subject to U.S. sanctions, notably the North Korean state-run military export company Changwang Sinyong, which has been cited three times before under the relevant law, the Iran Nonproliferation Act of 2000.