"The United States assists Taiwan in meeting its legitimate self-defense needs," said State Department spokesman Sean McCormack, arguing that the missile sale fell within US legislation governing US-Taiwan relations.

"The Bush administration remains fully committed to fulfilling the security and arms sales provisions of the Taiwan Relations Act," he said.

Under the act, passed when Washington switched its political recognition from Taipei to Beijing in 1979, the United States is committed to providing Taiwan with defensive weaponry.

"We believe that the sale in question is consistent with our responsibilities in that policy," McCormack said.

China's foreign ministry earlier Friday demanded the immediate cancellation of the sale of about 450 air and ground defense missiles to Taiwan and warned the transaction risked "harming the peace and stability of the Taiwan Straits and Sino-US relations".

It also said the sale would violate US commitments recognizing a single China with Beijing as its capital.

McCormack dismissed China's complaint, saying "they apparently do this on a regular basis concerning US arms sales to Taiwan.

"When they do so, we explain that US arms sales are consistent with our one-China policy," he said.

China considers Taiwan a part of its territory, to be reunified by force if necessary.