The U.S. government has imposed sanctions on three Chinese firms and a Chinese citizen accused of violating American restrictions on supplying Iran (search) with weapons-related goods or technology, the U.S. Embassy said Thursday.

The announcement didn't specify what the companies supplied, but said it might help Iran develop long-range missiles or nuclear, chemical or other weapons.

The latest penalties raise to 28 the number of Chinese companies or individuals sanctioned by Washington (search) after being accused of violating U.S. or international controls on transfers of weapons technology to Iran, Pakistan and other countries.

Asked about the sanctions at a regular news briefing, Chinese Foreign Ministry spokeswoman Zhang Qiyue didn't comment on the latest cases, but said, "China is opposed to the United States using its domestic laws to impose sanctions on Chinese companies."

Zhang said Beijing would impose its own punishment on any Chinese companies caught violating controls on weapons exports.

"China stands firmly against proliferation of weapons of mass destruction," Zhang said.

The latest companies sanctioned are barred for two years from doing business with the U.S. government or buying American goods that require export licenses, according to a U.S. Embassy spokeswoman.

Details of the accusations were withheld for intelligence reasons, the spokeswoman said on customary condition of anonymity.

The companies were identified as Liaoning Jiayi Metals and Mineral Co. Ltd., Wha Cheong Tai Co. Ltd. and Shanghai Triple International Ltd. The individual was identified as Q.C. Chen.

Also sanctioned was a North Korean company, Changgwang Sinyong Corp.

Chen has been targeted by U.S. sanctions twice in the past on similar accusations — in January and May 2002 — but Washington hasn't released any details of his identity.

Beijing is under pressure to stop what U.S. officials say is the transfer of missile and weapons technology by Chinese companies to Iran, Pakistan and other countries.

Asked in Washington whether the latest sanctions indicated that China was failing to keep pledges to do so, U.S. State Department spokesman Adam Ereli said, "There's definitely a ways to go."

Beijing has been trying to promote an image of itself as a responsible nuclear power and a partner in keeping weapons technology out of the hands of terrorists and rogue governments.

China isn't a member of the U.S.-led Missile Technology Control Regime — a 34-nation coalition to limit the spread of long-range missiles — but has promised to abide by its restrictions.

In May 2003, Washington sanctioned China's biggest state-owned weapons maker, Norinco, after accusing it of aiding Iran's long-range missile program. The company denied the accusation.