North Korea will pursue its "defensive" nuclear program as long as it feels threatened by the United States, its U.N. disarmament envoy in Geneva told Reuters on Thursday.

In a rare interview, Ambassador So Se Pyong also denounced the latest joint U.S.-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 II.

"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.