China has protested Washington's decision to impose sanctions on eight Chinese companies it accuses of helping Iran with its missile programs, saying there was no evidence showing any violations.
The US State Department told the Chinese companies early this month they would be prohibited from doing business in the US.
The Chinese companies also cannot get licenses that allow them to export or obtain patents for American technologies.
A North Korean company was also penalized.
"We cannot accept this and we are adamantly opposed," Foreign Ministry spokesman Kong Quan (孔泉) said on Tuesday during a regular news briefing.
"The US government has wantonly launched sanctions against Chinese companies without any evidence," he said.
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.
"China stands firmly against proliferation of weapons of mass destruction," Kong said. "What the Chinese government says, it does."
The US government has not detailed what the Chinese companies are alleged to have done but instead has focused on its concern over Iran's longer-range ballistic missiles and its alleged pursuit of nuclear weapons.
The matter is a sensitive diplomatic issue because China is a key partner of the US in the Bush administration's efforts to persuade North Korea to abandon its nuclear program.
One of the companies receiving sanctions was Norinco, China's biggest state-owned weapons maker, the New York Times reported.
In May 2003, Washington sanctioned Norinco after accusing it of aiding Iran's long-range missile program. The company denied the accusation.
Other firms identified by the newspaper as among the eight were the China Great Wall Industry Corp and the China Aero-Technology Import and Export Corp. The State Department placed a notice in the Federal Register early this month listing the Chinese companies affected.
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 is not a member of the US-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.