America wants to clamp down financially on four Iranian companies suspected of connections to Tehran's nuclear program.
It marked the government's latest move to put the financial squeeze on Iran, a country the United States accuses of fostering terrorism and whose nuclear ambitions have drawn international rebuke.
The Treasury Department's action is against Pars Tarash, Farayand Technique, Fajr Industries Group and Mizan Machine Manufacturing Group.
The action means that any bank accounts or other financial assets belonging to these three companies found in the United States must be frozen. Americans also are prohibited from doing business with them.
"So long as Iran continues to pursue a nuclear program in defiance of the international community's calls to halt enrichment, we will continue to hold those responsible to account for their conduct," said Stuart Levey, the department's undersecretary for terrorism and financial intelligence.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969