The penalties were imposed for the transfer of "equipment and technology controlled under multilateral export control lists or otherwise having the potential to make a material contribution to the development of weapons of mass destruction or cruise or ballistic missile systems," the State Department said.

"There was credible information that these entities had transferred one of several categories of items to Iran since January of 1999," spokesman Richard Boucher told reporters, adding that 23 companies and individuals were now subject to similar sanctions.

The sanctions include a bar on the firms and individuals doing business with the US government, a ban on US assistance and the automatic denial of US export licenses to them, he said.

Boucher would not elaborate on the specifics of the alleged sales which are punishable under the Iran Nonproliferation Act of 2000.

Many of the companies, in particular the Chinese and North Korean firms, have been under US sanctions for previous transgressions and are unlikely to be significantly affected by the new penalties.

The firms and individuals identified by the department in a Federal Register notice are:

The Beijing Institute of Aerodynamics of China, the Beijing Institute of Opto-Electronic Technology (BIOET) of China, Belarus Belvneshpromservice of Belarus, the Changgwang Sinyong Corporation of North Korea, the China Great Wall Industry Corporation of China, China North Industries Corporation (NORINCO) of China,

Dr C Surendar and Dr YSR Prasad of India, Khazra Trading of Russia, the LIMMT Economic and Trade Company of China, Oriental Scientific Instruments Corporation (OSIC) of China, South Industries Science and Technology Trading Company of China, Telstar of Spain, and the Zaporizhzhya Regional Foreign Economic Association of Ukraine.