GENEVA - North Korea will pursue its "defensive" nuclear program as long as it feels threatened by the United States, its UN disarmament envoy in Geneva told Reuters on Thursday.In a rare interview, Ambassador So Se Pyong also denounced the latest joint US-South Korean military exercises, due to start next week, saying they fanned tensions on the divided peninsula as it marks the 70th anniversary of liberation from Japanese occupation at the end of World War Two."They have to change their attitude, their hostile policies attitude and otherwise ... We'll continue the simultaneous development of the economy and the nuclear program," he told Reuters, speaking English."It is to make a balance with the United States. It's totally defensive, that is 100 percent sure. But once they do something then we'll do the same. If they break (out in) another war, we are ready to make any kind of things," said So, who is the Democratic Republic of Korea's ambassador to the United Nations in Geneva and to its Conference on Disarmament.