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North Korea would be making a "huge mistake" if it launched one of its medium-range missiles during the current standoff between it, the United States and South Korea, Mr Kerry warned.

Mr Kerry is discussing the crisis with President Park Geun-hye and his South Korean counterpart as well as US military commanders in the country.

North Korea will gain nothing by threatening tests of its missile or nuclear programs, Mr Kerry said, emphatically stating the U.S. and its Asian ally won't accept the North as a nuclear power.

The US Secretary of State warned that North Korean leader Kim Jong-un needs to understand "what would be the outcome of any conflict."

If North Korea were to launch missiles "it would contribute to an already volatile, potentially dangerous situation," he added.

Mr Kerry said US preference would be to get into talks on the North Korean nuclear issue "to ultimately diffuse the situayion," but the reclusive state must be serious about denuclearisation.

South Korean Foreign Minister Yun Byung-se called Pyongyang's threats a "grave provocation" to the entire international community.