Pyongyang has made clear its nuclear weapons are no longer negotiable but its strategy can be recalibrated depending on Washington’s approach.

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.