WASHINGTON --- U.S. and South Korean defense officials reaffirmed the two nations commitment to keep the defense alliance strong and to continue transforming to meet 21st-century defense needs.> Defense Secretary Robert M. Gates and South Korean National Defense Minister Lee Sang-hee spoke at the conclusion of the 40th U.S.-Republic of Korea Defense Consultative Talks here.>> North Korea remains the threat in the region, and the United States reaffirmed its commitment to defend the republic including extending the U.S. nuclear umbrella to the country, Gates said.>> The Mutual Defense Treaty between the United States and South Korea is a vibrant reflection of the common values and aspirations of our peoples, the secretary said. It remains vital to the interests of both of our nations and will continue to be the foundation for an enduring resolute and capable defense of the Republic of Korea.>> Gates said the North Korean nuclear and conventional threats continue to be focal points of the treatys deterrent and defense posture.>> We urge a swift resolution to the North Korean nuclear issue through the Six-Party Talks process, he said. The talks with South Korea, China, Russia, Japan and the United States seek to engage North Korea and convince the leaders of the repressive state to shut down its nuclear weapons production system and stop proliferation of weapons of mass destruction.>> Gates thanked Lee for his countrys support in Iraq and Afghanistan. South Korea has sent troops that have contributed significantly to stability and reconstruction.