The Pentagon announced Tuesday that the United States mistakenly shipped to Taiwan four electrical fuses designed for use on intercontinental ballistic missiles, but has since recovered them.

The error is particularly disturbing, officials said, because of its indirect link to nuclear weaponry and because of the sensitivity of U.S. arms sales to Taiwan, which China regularly denounces as provocative. The Defense Department said an investigation of the incident is under way.

At a news conference, Air Force Secretary Michael Wynne said the misshipped items were four electrical fuses for nose cone assemblies for ICBMs. He also said they were delivered to Taiwan in 2006 and had been sent instead of helicopter batteries that had been ordered by Taiwan.

Wynne said the investigation is meant to sort out what happened and how.

President Bush was briefed about the mistaken shipment and is glad that the parts have been recovered, said White House press secretary Dana Perino.

"He appreciates that they are taking action, and that there is a full investigation under way," Perino said.

Asked if Bush still has confidence in Air Force leadership, Perino said: "Yes, yes he does."

The fuses were manufactured for use on a Minuteman strategic nuclear missile but contained no nuclear materials.

It is the second nuclear-related mistake involving the Air Force in recent months. Last August an Air Force B-52 bomber was mistakenly armed with six nuclear-tipped cruise

Henry said the exact sequence of events that led to the mistake and the recovery of the items was unclear.

U.S. arms sales to Taiwan are especially sensitive because China vehemently objects to U.S. defense assistance to the island that Beijing deems to be part of China.

Taiwan, which split from China amid civil war in 1949, potentially is the most sensitive issue in U.S.-China relations. Beijing claims Taiwan as its own and has threatened to attack should the self-governing island make its de facto independence formal. Washington has hinted that it would go to war to protect Taiwan.

While Washington switched its recognition from Taipei to Beijing in 1979, it remains the island's most important foreign backer, providing it with the means to defend itself against a possible Chinese attack.