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

"We're certainly not going to stand by idly while weapons proliferation programs are assisted," the State Department's deputy spokesman Adam Ereli told reporters.

Three of the five entities have been imposed penalties 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.

"It's an uphill battle. But I think the administration has rightfully pointed to proliferation as a major concern," he added.

Andrew K. Semmel, acting assistant secretary of state for nonproliferation, said in a statement that 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.

No new licenses would be granted for transfer to the blacklisted entities of items controlled under export laws. Existing licenses would be suspended.

The three entities slapped 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).

Individual agent Q.C. Chen and the North Korean firm had been slapped with multiple sanctions previously.

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

"It's a work in progress."

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

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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