BEIJING - China expressed concern and dissatisfaction with the United States on Wednesday after the Pentagon said it mistakenly shipped four fuses for nuclear missiles to Taiwan in 2006.

Beijing had urged the United States to thoroughly investigate and report the details promptly to China so as to "eliminate the negative effect and severe consequences," Foreign Ministry spokesman Qin Gang was quoted on a ministry Web site as saying.

"We express our serious concern and strong dissatisfaction with this and have made solemn representations to the American side," he said.

Beijing believes self-ruled Taiwan, which held a presidential election on Saturday, is part of China and has declined to renounce the use of force as a means to reunite the island with the mainland.

The U.S. military was supposed to ship helicopter batteries to Taiwan, but instead sent fuses used as part of the trigger mechanism on Minuteman missiles, the Pentagon said on Tuesday. Taiwan returned the parts to the U.S. last week.

No nuclear material was shipped to Taiwan, Pentagon officials said.

Taiwan's Defence Ministry confirmed the parts had already been returned, and that they were seeking damages.

"Taiwan-U.S. military cooperation has always been close, and this was a case of mistaken shipment," it said in a statement. "It will not affect continuing future bilateral relations."

The problem went unnoticed until Taiwan realized it did not have the helicopter batteries it ordered and reported the issue to the United States, U.S. officials said.

Chinese Foreign Ministry spokesman Qin repeated China's calls for the United States to stop arms sales and joint exercises with Taiwan in order to avoid upsetting peace and stability and keep Sino-U.S. relations healthy.

The U.S. has not had diplomatic relations with Taipei since 1979 but is bound by law to help Taiwan defend itself.

Comment: Wonder who made that law. The US perhaps.

The erroneous fuse shipment was the Pentagon's second embarrassing misplacement of nuclear or nuclear-related equipment announced in recent months. An Air Force bomber mistakenly carried nuclear warheads over the United States in August 2007.

It was unclear what led to the fuse shipment and the Pentagon does not yet know who was responsible.

The fuses, which send an electronic signal to the device that starts the nuclear weapon's trigger process, are among a class of sensitive equipment that must be accounted for on a quarterly basis.

Based on the information now known, the four fuses, which do not resemble helicopter batteries, were wrongly placed in an unclassified storage area. They were then shipped in late 2006 to Taiwan, which placed them in storage.

When Taiwan realized it had received the incorrect shipment, it notified the U.S. military.

(Reporting by John Ruwitch, Ben Blanchard in Taiwan; Editing by David Fox)