The Taiwan warhead issue "came up very briefly" in the telephone conversation between Bush and Hu, national security advisor Stephen Hadley told reporters.

"And, basically, the president (Bush) indicated that a mistake had been made. There was very little discussion about it," Hadley said.

The issue "was a very small part of the conversation," Hadley added.

The erroneous shipment of the fuses, which can be used to trigger warheads on ballistic missiles, was only discovered last week, the Pentagon said on Tuesday.

China on Wednesday expressed concern over the revelation and demanded a probe be launched.

"We express our serious concern and strong dissatisfaction and demand the US side investigate this incident," foreign ministry spokesman Qin Gang said in a statement.

"We urge the US to cease selling military hardware to Taiwan and end US-Taiwan military ties, or risk harming stability in the Taiwan Strait and the healthy and stable development of China-US ties," the spokesman said.

Nose cone assemblies containing the fuses were recovered on Monday from Taiwan where they had been held in storage after being shipped there as helicopter batteries, senior Pentagon officials said.

The fuses are housed in nose cones that are fitted to the warhead of a Minuteman intercontinental ballistic missile. They are used to ignite the trigger of a Mark-12 nuclear weapon, US officials said.

US Defense 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, the 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.

The Taiwanese received the fuses in 2006, then informed the US side that they had not received the batteries they had ordered for their helicopters. The US officials thought they were talking about different sorts of batteries.

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