President Barack Obama's choice to lead U.S. forces in the Pacific warned Thursday that North Korea's missile and nuclear threats could spark an arms race in Asia.

Admiral Robert Willard also told senators at his confirmation hearing that China's huge military buildup remains a serious worry for the U.S. military.

North Korea's recent missile and nuclear tests and belligerent rhetoric aimed at the United States, Japan and South Korea have had northeast Asia on edge for months.

Willard said North Korean actions pose a significant threat to the United States and its allies and "could spur a limited arms race as neighbors seek to enhance their own deterrent and defense capabilities."

The North carried out its second nuclear test in May. On Saturday it test-fired a barrage of ballistic missiles into waters off its east coast, its biggest display of missile firepower in three years. The North deploys hundreds of missiles that have all of South Korea and Japan within their striking range.

During the hearing, lawmakers also questioned Willard about North Korea's intentions and about the frail appearance Wednesday of North Korean leader Kim Jong Il, who reportedly suffered a stroke last year.

Willard said that Kim's ill health, questions about a successor, and a change of administration in South Korea, where a new conservative leader has infuriated Pyongyang, may be contributing to the North's provocative actions.

The U.S. military, Willard said, stands ready to defend the United States should Kim follow through on threats to attack.

On China, Willard spoke of "major concerns" about the uncertainty surrounding Beijing's development of advanced weapons that are "beyond what is required for its national defense." He said he would pursue "careful, measured military engagement" with China to reduce the chance of miscalculation and to press for transparency on military spending.

China and the U.S. have recently resumed military consultations after Beijing suspended talks in anger over American arms sales to Taiwan, the self-ruled island that China claims as part of its territory.

The United States questions China's nearly 20 years of annual double-digit percentage increases in its defense budget; Beijing says any worries are unfounded.

China's emergence as a "constructive partner in regional security" is crucial, Willard said, and U.S.-Chinese talks are important to encouraging cooperation and addressing differences.

Even as China deals with ethnic unrest in its western region, Willard said, it should exert its influence on North Korea to stop its recent provocations.