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

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 said on Saturday its nuclear weapons are not meant for negotiations but are intended for combat use against enemies that threaten its people and world peace, its state media reported.