Treasury action prohibits the designated 37 companies, as well as five Iranian individuals, from doing business with the US [AFP]

The US has blacklisted 37 shipping companies in Germany, Malta and Cyprus that Washington says are linked to Iran's nuclear programme.

The Treasury Department said the "front companies" were facilitating Iran's use of its national maritime carrier to advance its illicit programme for developing weapons of mass destruction and for transporting military cargo.

Wednesday's Treasury action prohibits the designated 37 companies, as well as five Iranian individuals, from doing business with the US 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 State 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."

The blacklisting is the latest in a series of actions by the United Nations and the United States and other countries to punish Iran for its disputed nuclear programme.

The latest action identified the 37 "front companies" as based in the ports of Hamburg, Germany; Sliema, Malta; and Limassol, Cyprus. The five Iranians were managers or directors of the firms.

The Iranian shipping company initially had been designated for sanctions in 2008. To date, nearly 70 IRISL front companies and affiliates have been targeted, the department said.

Experts generally have 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.