The Pentagon has admitted it mistakenly sent Taiwan four fuses used to trigger nuclear warheads on ballistic missiles in late 2006 and only discovered the mistake last week.

The fuses were recovered on Monday from Taiwan, where they were believed to have been held in storage after being mistakenly shipped as helicopter batteries from a Defence Department logistics facility in the United States, senior Pentagon officials said.

US Defence Secretary Robert Gates has ordered an investigation into the incident and a comprehensive review of the US inventory of all nuclear-related components as well as of policies and procedures, senior officials said.

"We'll do a thorough investigation, and those who are responsible will be held accountable. The secretary is quite forceful on this," said Ryan Henry, principal deputy undersecretary of defense for policy.

It was the second major nuclear security breach uncovered in just over six months, following the mistaken transfer of nuclear-armed cruise missiles from one US base to another aboard a B-52 bomber in September.

Investigators will seek to determine whether the fuses and nose cone assemblies in which they were housed were tampered with, as well as how the error occurred and who was responsible.

China was notified of the shipment, Mr Henry said.

"Our policy on Taiwan arm sales have not changed. This specific incident was an error in process only and is not indicative of our policies, which remain unchanged," he said.

- AFP