US President Barack Obama on Tuesday reaffirmed the US commitment to defend South Korea after talks with visiting President Lee Myung-Bak, at a time of escalating threats from North Korea. "We have reaffirmed the endurance of our alliance and America's commitment to the defence of the Republic of Korea," Obama said in an a press appearance with Lee in the White House Rose Garden. Lee said that the US assurances included the US nuclear umbrella in East Asia.