New prohibitions and the potential freezing of assets were announced against alleged senior officers in the Guard Corps, an elite branch of Iran's military, and members of the affiliated Qods force, which conducts special overseas operations and liaison with terrorist groups.
Both the Bush and Obama administrations have pursued global sanctions against Iran to thwart its nuclear ambitions.
"Today we are announcing a set of actions that highlight another of the IRGC's dangerous pursuits, its support of terrorism," said Stuart Levey, treasury undersecretary for terrorism and financial intelligence.
The announcement came as the Obama administration is embarked on an international campaign to tighten sanctions on Iran and North Korea and ensure that recently passed United Nations sanctions on Iran are strictly implemented.
A top U.S. nonproliferation official, Robert Einhorn, met with South Korean officials this week in Seoul, urging them to crack down on trade with Iran. On North Korea, he said the United States soon would announce new measures targeting that country's ability to procure conventional arms, import luxury goods and allegedly counterfeit U.S. currency.
The impact of both efforts could be weakened significantly if China moves to fill the gap left by others' departure from Iran's markets.
"We want China to be a responsible stakeholder in the international system. And that means . . . not backfilling, not taking advantage of the responsible self-restraint of other countries," Einhorn said in Seoul.
On Tuesday, the Treasury targeted four senior Qods officers for their support of terrorism, as well as Iranian individuals or organizations thought to support terrorism efforts in Lebanon, Syria and Afghanistan.
This support, often under the guise of reconstruction or economic development, allegedly went to groups such as Hezbollah, Hamas, Palestinian Islamic Jihad, the Popular Front for the Liberation of Palestine-General Command and the Taliban in Afghanistan. The U.S. government has designated all but the Taliban as terrorist organizations.
Levey also identified 21 entities the Iranian government allegedly owns or controls, including two banks in Belarus and nine companies in Germany, a stalwart U.S. ally.
Two of the German-based companies are said to be investment arms of the state-owned Iran Foreign Investment Co. The others are involved in mining, metals and machinery, but Iran may be seeking their products to help develop its nuclear program.
"Dual use is the word that comes to mind immediately. I didn't believe for one second that there was concern about the Iranian mining industry," said Patrick Clawson, deputy director of research for the Washington Institute for Near East Policy, a policy organization sympathetic to Israel. "Purely the sniff test, this looks nuclear to me."
Clawson pointed to earth-moving equipment Iran imported from Germany to build subway tunnels. The U.S. government thinks it also was used to build tunnels at secret underground nuclear facilities.
The German Embassy in Washington had no immediate comment on the Treasury action.
David Albright, a nuclear proliferation expert at the Washington-based Institute for Science and International Security, said Germany had been "quite good" in controlling nuclear-related trade with Iran.
"But they do a lot of business with Iran, and I think that's what the U.S. is focusing on now, this extra business that isn't nuclear," said Albright, who was in Germany on Tuesday and hadn't seen the announcement. The government of Chancellor Angela Merkel has tried to curb German trade with Iran and "the companies, many of them, are pushing back."
Many of the targeted Germany-based companies are affiliates of Ascotec Holding, a Dusseldorf company that trades in metals, minerals and machinery. The Treasury described all these companies as "determined to be owned or controlled by the government of Iran."
It didn't take much to make that determination.
On its website, the company boasts "From Iran into the world." A click on its "company" link connects to a flow chart that shows the Iranian Ministry of Industries and Mines as the owner of the Iranian Mines and Mining Industries Development and Renovation Organization, which in turn owns Ascotec. Other companies the Treasury listed appear on the flow chart or elsewhere on the website.
Two affiliated companies on Ascotec's website apparently were excluded from action Tuesday: United Steel Co. in Kuwait and Ascotec China, said to have opened in 2008.
Although it's illegal to trade with Iran, Treasury officials said the identification of the firms helped alert U.S. companies.
West Sun Trade, also cited Tuesday, was said to be based in the German city of Hamburg. However, in a profile on www.alibaba.com, it called itself a Dubai-based company that's operated in Germany since 1990, trading in raw materials.
The European Union approved tough sanctions on Iran last week, including a ban on new investment in the oil and gas sector and on most insurance and reinsurance, and a prohibition on cargo flights to EU countries by Iranian carriers.
A European official said the international sanctions were crimping Iran's efforts to modernize its energy industry and raising the cost of imports by 20 per cent to 25 per cent.
"It's given them something to think about," said the official, who insisted on anonymity to discuss diplomatic calculations. "My reading is, they are nervous."