North Korean leader Kim Jong Un gives field guidance to the Taedonggang Terrapin Farm in this undated photo released by North Korea’s Korean Central News Agency (KCNA) in Pyongyang on Tuesday.

The United States on Wednesday dismissed a claim by North Korea to have developed the ability to miniaturize nuclear warheads, but voiced concern Pyongyang was developing long-range missiles.

“Our assessment of North Korea’s nuclear capabilities has not changed. We do not think that they have that capacity” to miniaturize weapons, a National Security Council (NSC) spokesman, Patrick Ventrell, told AFP.

North Korea ramped up its nuclear threats on Wednesday, boasting it had mastered the ability to deliver miniaturized warheads on high-precision long-range rockets.

Reducing the size of a nuclear warhead to the point where it can fit on a long-range missile would be a major leap forward in offensive capability, and Pyongyang has claimed progress with miniaturization before.

Ventrell agreed Pyongyang was “working on developing a number of long-range missiles, including intercontinental ballistic missiles, that could eventually threaten our allies and the homeland.”

“That is why the administration is working to improve regional and homeland missile defenses and continuing to work with the other members of the six-party talks to bring North Korea back into compliance with its nonproliferation commitments,” he said.

Pyongyang’s claim came only days after a visit by top US diplomat John Kerry to Seoul when in a stinging assessment he slammed Kim Jong-Un’s “egregious” leadership and “grotesque” executions and warned of possible new sanctions.

The North on Wednesday denounced what it called Kerry’s “reckless” remarks and canceled an invitation to UN Secretary General Ban Ki-Moon to visit a joint industrial zone on its side of the border with South Korea.

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