At a Pentagon news conference, Air Force Secretary Michael Wynne said the mis-shipped 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.
The fuses were manufactured for use on a Minuteman strategic nuclear missile but contain no nuclear materials.
"This could not be construed as being nuclear material. It is a component for the fuse in the nosecone for a nuclear system," Wynne said. "We are very concerned about it."
Wynne said the matter is under investigation. He said the Taiwanese authorities notified U.S. officials of the mistake. He said the fuses had been in a shipping container sent from one U.S. Air Force base to another in 2005 and then delivered to Taiwan in 2006.
The Chinese Embassy did not immediately respond to a request for comment. A Taiwan official said Tuesday that the island's diplomats in Washington typically do not comment on Defense Department matters.
Ryan Henry, the No. 2 policy official in the office of Defense Secretary Robert Gates, said President Bush was notified of the mistake and the actions to recover the items. Henry called the mistake "disconcerting" and intolerable. He said the Chinese government has been notified of the error.
Henry said an examination of the site in Taiwan where the components had been stored after delivery indicated that they had not been tampered with. He said the components were "quite dated," as part of a system designed in the 1960s.
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.
The United States follows a "one China" policy that recognizes there is a single China and that self-ruled Taiwan is part of it. 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.
China and Taiwan split amid civil war in 1949. Beijing continues to claim the island as part of its territory and has threatened to attack if Taiwan formalizes its de facto independence.