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.

The North Korean leader said the partnership poses a grave threat to his country and vowed to further bolster his nuclear weapons program.

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

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North Korea's Kim Jong Un criticizes the trilateral military cooperation between the United States, Japan and South Korea for only increasing tensions