"The United States does not follow international practices in punishing the enterprises. We request that they should stop," foreign ministry spokesman Kong Quan told a regular briefing.

Kong did not specify what companies he was referring to, or what kind of proliferation they were accused of engaging in.

The US State Department earlier this year announced a number of Chinese companies were being penalized for transferring to Iran "equipment and technology controlled under multilateral export control lists."

"There are some accusations on China's efforts regarding non-proliferation. We don't think those accusations are based on facts," Kong said.

"Everybody knows China has formulated a series of very strict regulations and laws on non-proliferation and export controls."

Kong, speaking ahead of expected new talks on North Korea's nuclear ambitions, repeated Chinese denials of any help to the secretive regime's atomic weapons program.

"We don't have any cooperation with North Korea on nuclear technology," he said.

Bush is expected in China on November 19 for meetings with his counterpart Hu Jintao.

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