Beijing on Thursday slammed the United States for sanctioning four Chinese companies suspected of helping Iran acquire weapons of mass destruction. "The US government did not provide any evidence before they froze transactions on the four Chinese companies. This is completely unreasonable and irresponsible," said Jiang Yu, a spokeswoman of the Chinese Foreign Ministry at a regular briefing. "We express our strong dissatisfaction and firm opposition." Washington on Tuesday prohibited U.S. companies from having any dealings with the Chinese companies as well as a U.S. company, claiming they helped Iran obtain weapons of mass destruction and missiles capable of delivering them. It said they supplied the country with missile-related and dual use components. "The Chinese government is firmly opposed to the proliferation of weapons of mass destruction and we do not allow any companies or individuals to support or engage in proliferation of any form," Jiang said. The Chinese companies targeted in the ban were Beijing Alite Technologies Company, Ltd.; LIMMT Economic and Trade Company, Ltd.; Great Wall Industry Corporation and China National Precision Machinery Import/Export Corporation. China National Precision's US representative, Torrance, California-based G.W. Aerospace, also had its transactions frozen. China has long rejected accusations that mainland companies have violated regulations against sharing international controls on transfers of weapons technology to Iran, Pakistan and other countries. It has also objected to US sanctions, saying that it would enforce its own laws if such violations are found. The US government has applied various sanctions against the four Chinese companies in the past. In 2004 the US State Department sanctioned all four in accordance with the Iran Nonproliferation Act of 2000 for transferring equipment and technology to Iran.