"The Chinese government attaches great importance to export control and law enforcement. We're also exerting effort to make sure that all the relevant regulations are implemented in real earnest," foreign ministry spokeswoman Zhang Qiyue said.

"If there are certain violations of Chinese companies and individuals, we will punish them according to law. However, in the meantime, we oppose other countries citing their domestic laws to impose sanctions on Chinese companies.

"We hope the US side can start from our cooperation on non-proliferation in other fields and not impose sanctions citing domestic laws," Zhang told a regular briefing.

The US State Department announced Wednesday that Washington has imposed sanctions on four Chinese companies, including a state-run firm, and one North Korean entity for selling weapons technology and equipment to Iran.

It vowed to step up a crackdown on dangerous weapons proliferators through "sustained and high-level engagement" with the Chinese government.

State Department deputy spokesman Adam Ereli said the United States was prodding China to develop export control regulations that would address the problem and enforce them in "a robust and systematic way so that we can get to the heart of it".

The three entities slapped with fresh restrictions were Q.C. Chen (China); Wha Cheong Tai Company Ltd (China) and Changgwang Sinyong Corporation (North Korea).

The alleged new offenders were Liaoning Jiayi Metals and Minerals Company, Ltd (China), reportedly a state-run economic entity, and Shanghai Triple International Ltd (China).

Three of the five entities have had penalties imposed previously for the transfer to Iran of equipment and technology controlled under multilateral missile, chemical and nuclear weapons' export regulations.

"There are unrepentant proliferators out there and it's going to require a concerted, sustained effort to fight them," Ereli said.

Two-year sanctions would be imposed against the five entities effective November 24 under the Iran Nonproliferation Act of 2000.

The sanctions, among other things, bar US government agencies from procuring goods, technology or services from the five and instantly terminates any defense contracts with them.

The United States has warned repeatedly that it would do whatever necessary to prevent Tehran from obtaining nuclear weapons and has stepped up vigilance on the movement of dangerous equipment or technology to Iran.

Iran and North Korea have been tagged as part of an "axis of evil" by US President George W. Bush.

The UN nuclear watchdog agency this week spared Iran from being referred to the UN Security Council for possible sanctions after Tehran agreed, in a deal with Britain, France and Germany, to suspend its uranium enrichment program.

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