Beijing ? China issued a vehement protest Wednesday over a mistaken shipment of U.S. nuclear missile fuses to Taiwan, demanding a thorough investigation and saying the incident had “disastrous consequences.”

The strong language reflected the depth of Chinese opposition to U.S. weapons sales to Taiwan, a self-ruled island that Beijing insists is a part of China. In particular, China has regarded with irritation a recent effort by the Taiwanese Defense Ministry to buy advanced F-16 warplanes to enhance its fleet of older F-16s bought from Washington a decade ago and Mirages acquired from France.

The Pentagon revealed Monday – two days after Taiwan’s presidential election – that its Defense Logistics Agency had in August 2006 accidentally shipped to Taiwan four nose-cone fuse assemblies designed to detonate nuclear warheads atop Minuteman intercontinental ballistic missiles. The fuses were dispatched in the belief that they were battery packs destined for Taiwan’s UH-1 Huey helicopter fleet, Pentagon spokesmen explained.

Bush administration officials said that the fuses had been returned and that U.S. diplomats had been in touch with China and Taiwan to explain the error since it was discovered last week. But the Chinese Foreign Ministry, in a statement, said it expected to be told in more detail what happened and declared the shipment could have “negative effects” on relations between Washington and Beijing.

“We demand that the U.S. side thoroughly investigate this matter and report to China in a timely manner the details of the situation and eliminate the negative effects and disastrous consequences created by this incident,” said a declaration attributed to Qin Gang, a ministry spokesman. “We urge the U.S. side to keep the promises they have made … and stop weapons sales and military contacts with Taiwan to avoid endangering peace and stability in the Taiwan Strait and the improvement in Sino-U.S. relations.”

Qin said China had made a “serious representation” to the United States over the shipment, which he said caused “strong displeasure” in President Hu Jintao’s government.

The United States has been Taiwan’s main protector since Chiang Kai-shek’s Nationalist forces fled there after their defeat by Mao Zedong’s Communist Party in 1949. Under the Taiwan Relations Act, it has pledged to help Taiwan defend itself. The pledge has been kept deliberately ambiguous, but its main manifestation has been regular weapons sales.

The Chinese government has just as regularly protested the sales, which it says violates understandings struck when the United States and China renewed diplomatic relations three decades ago.

Taiwan has no known nuclear weapons program, and the fuses would be of no known use to its Defense Ministry. At the same time, the island’s government mounted a nuclear weapons research program at one point, and the issue remains extremely sensitive in China.

In addition, Chinese officials have come under heavy criticism over the past week because of rioting and a subsequent security crackdown in Tibet, leaving them in no mood to gloss over the Pentagon’s error in their public statements.