Putting a new squeeze on Iran, the Obama administration on Wednesday blacklisted 37 shipping companies in Germany, Malta and Cyprus that the U.S. says are linked to Tehran's nuclear program.
The Treasury Department said all are front companies owned or acting for the Islamic Republic of Iran Shipping Lines, which the department said are used to advance Iran's nuclear and missile programs.
The blacklisting is the latest in a series of actions by the U.N., as well as the U.S. and other countries to punish Iran for its disputed nuclear program. They are also supposed to pressure Tehran into agreeing to taking steps to prove that the program is not used to make bombs.
Experts have generally agreed the sanctions are taking a toll on Iran, but many doubt the pressure will compel Tehran to cede to international demands to give up its nuclear ambitions.
Iran said its nuclear program is entirely for peaceful uses. The U.S. and some others think it is intended to give Iran the capability to build weapons.
At the State Department, spokesman P.J. Crowley said the administration is willing to revive a proposal under which Iran would ship abroad most of its low-enriched uranium to be turned into fuel for a research reactor.
A deal along those lines was tentatively arranged a year ago, but Iran ultimately rejected it and declined repeated offers to return to negotiations.
"We still think the concept has a potential value," Crowley said. "So we would be interested in continuing to pursue that ... with Iran if Iran is interested."
He said the arrangement would have to be "updated" to reflect the fact that Iran has produced additional enriched uranium in the year since the deal was first negotiated in Geneva.
Crowley said Iran so far has not accepted an offer by the European Union's foreign affairs and security chief, Catherine Ashton, to meet for three days in mid-November in Vienna to discuss nuclear issues. Also participating would be the U.S., Britain, China, France, Russia and Germany.
Wednesday's Treasury action prohibits the designated 37 companies, as well as five Iranian individuals, from doing business with the U.S. and is designed to discourage other countries from doing business with them.
"We will continue to expose the elaborate structures and tactics Iran uses to shield its shipping line from international scrutiny so that it can continue to facilitate illicit commerce," said Stuart Levey, the department's undersecretary for terrorism and financial intelligence.
"This pattern of obfuscation is leading the private sector around the world to refuse business with Iran rather than risk becoming involved in its nuclear and missile programs."