The Bush administration has quietly applied new sanctions against eight Chinese companies for helping Iran (search) with its missile programs, the White House spokesman said Tuesday.

Administration officials confirmed a report in The New York Times that said the State Department had served notice to the Chinese firms early this month. A North Korean company was also penalized.

The sanctions prohibit the companies from doing business in the United States, and ban them from obtaining licenses that allow them to export or obtain a patent for American technologies.

"We have long had concerns about Iran's development of longer-range ballistic missiles (search) and Iran's pursuit of nuclear weapons," White House press secretary Scott McClellan said. "The penalties mean the companies will not be able to do business with U.S. government departments or agencies, and that American technology cannot be exported to the companies."

McClellan did not elaborate on why the Chinese firms had drawn U.S. ire, focusing instead on the administration's concerns about Iran. The matter is a sensitive diplomatic issue because China (search) is a key partner of the United States in the Bush administration's efforts to persuade North Korea (search) to abandon its nuclear program.

One of the companies receiving sanctions was Norinco (search), China's biggest state-owned weapons maker. 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. (search) and the China Aero-Technology Import and Export Corp (search).

Norinco also manufactures military-style semiautomatic assault weapons.

The State Department placed a notice in the Federal Register (search) early this month listing the Chinese companies affected.

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

"Proliferation is an issue we take very seriously, and stopping it has been a top priority for the president," McClellan said.