WASHINGTON (CNN) -- The U.S. Defense Department accidentally shipped ballistic missile components to Taiwan, the Pentagon said Tuesday.

A U.S. Defense Department image shows the missile components it says were accidentally shipped to Taiwan.

Four nose-cone fuses for intercontinental ballistic missiles were shipped instead of the helicopter batteries that Taiwan had requested, Air Force Secretary Michael Wynne said.

The fuses were shipped to Taiwan in fall 2006 and kept in a warehouse there. The Taiwanese military informed the United States last week about their presence on the island.

"There are no nuclear or fissile materials associated with these items," Wynne said. "The United States is making all appropriate notifications in the spirit of candor and openness in an effort to avoid any misunderstanding." Watch Wynne describe the fuses »

An investigation is under way, he added. Watch how missile parts ended up in Taiwan »

Ryan Henry, principal deputy undersecretary of defense for policy, said, "In an organization as large as DOD, the largest and most complex in the world, there will be mistakes. But they cannot be tolerated in the arena in strategic systems, whether they are nuclear or only associated equipment, as was in this case."

Henry said the parts were 1960s technology, designed for use with Minuteman ballistic missiles.

Officials said China, which considers Taiwan to be a renegade province, has been notified about the mistake.

The Chinese government did not immediately issue a response to the news.

Wynne said the missile components were first shipped from F.E. Warren Air Force Base in Wyoming to Hill Air Force Base in Utah in 2005.

On arrival at Hill, they should have been placed in the classified storage section, Wynne said, but instead were moved to a storage area for unclassified items.

He said stocks at the Utah base should be checked quarterly and a key part of the investigation will be determining how those checks did not turn up the missile parts before they were shipped to Taiwan.

It is the second nuclear-related mistake involving the Air Force in less than a year. In August, a B-52 bomber mistakenly carried six nuclear warheads from North Dakota to Louisiana. A six-week investigation uncovered a "lackadaisical" attention to detail in day-to-day operations at the air bases involved.

The Air Force said it relieved four officers, including three colonels, and other personnel lost their certification to handle sensitive weaponry. E-mail to a friend

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