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

SEOUL (Reuters) -North Korean leader Kim Jong Un criticised trilateral military cooperation among the United States, Japan and South Korea for raising tensions in the region and vowed countermeasures,

Leader Kim Jong Un pledged to pursue "sustained countermeasures," citing security ties between the U.S. and its regional allies.

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.