North Korean leader Kim Jong Un said an elevated US security partnership with South Korea and Japan poses a grave threat to his country and vowed to bolster his nuclear weapons program further, state media reported Sunday.

Reuters, the news and media division of Thomson Reuters, is the world’s largest multimedia news provider, reaching billions of people worldwide every day. Reuters provides business, financial, national and international news to professionals via desktop terminals, the world's media organizations, industry events and directly to consumers.

North Korean leader Kim Jong Un has vowed to bolster his nuclear weapons program in response to the U.S.’s enhanced security partnership with South Korea and Japan. Last year, the U.S. expanded bilateral military exercises with South Korean and trilateral training with South Korea and Japan.

North Korea has vowed to keep developing nuclear weapons in response to U.S. cooperation with South Korea and Japan.