The US has imposed sanctions on nine foreign companies, six of them Chinese, for allegedly selling missile goods and chemical arms material to Iran.
The US is keen to stop other states aiding Iran's weapons programmes
A US State Department spokesman said the measures were based on "credible evidence" but gave no details.
The US will not provide export licences to the firms involved, two of them Indian and one Austrian, and has banned the US government trading with them.
China has in the past denied selling weapons-related material to Iran.
The US and EU suspect Iran of pursuing nuclear weapons and are considering whether to refer it to the UN Security Council. Tehran says its nuclear programme is for civilian energy use.
Washington said it had taken action against the companies concerned under the Iran Non-proliferation Act, passed by the US Congress in 2000.
The legislation aims to prevent international support for Iran's nuclear, chemical and missile-based weapons programmes.
US state department spokesman Adam Ereli, quoted by the Associated Press news agency, said: "It's an important and effective tool in constraining Iran's efforts to develop missile and weapons of mass destruction capabilities.
"It does have an impact, particularly in alerting governments to activity taking place in their countries."
He named the Chinese companies involved as: China Aerotechnology Import Export Corporation, the missile exporter China North Industries Corporation, Zibo Chemet Equipment Company, the Hongdu Aviation Industry Group, Ounion International Economic and Technical Cooperative Limited and the Limmt Metallurgy and Minerals Company.
The two Indian companies are Sabero Organics Chemical and Sandhya Organics Chemical and the Austrian firm is Steyr-Mannlicher, which makes assault weapons.
The penalties against the firms will remain in place until December 2007.
A CIA report to Congress last year said Iran was seeking to buy material for nuclear and chemical weapons programmes from private firms in Russia, China, North Korea and Europe.