John Kerry: North Korea will be making huge mistake if it launches a missile

Mr Kerry was speaking at the start of four days of talks in east Asia. He also plans to visit China and Japan. He said Pyongyang and its enigmatic young leader would only increase their isolation if they launched the missile, which has a range 2,500 miles — enough to reach the US territory of Guam: “If Kim Jong-un decides to launch a missile, whether it’s across the Sea of Japan or some other direction, he will be choosing wilfully to ignore the entire international community. And it will be a provocation and unwanted act that will raise people’s temperatures.

“It will further isolate his country and further isolate his people, who are desperate for food and not missile launches. They are desperate for opportunity and not for a leader to flex his muscles.”

Mr Kerry met South Korean president Park Geun-hye and was to have talks with the chiefs of the 28,000-strong US military presence in the country.

As he arrived, an assessment by the Pentagon’s defence intelligence agency said North Korea has advanced its nuclear knowledge to the point that it could arm a ballistic missile.

Mr Kerry played down this report. Pentagon spokesman George Little said “it would be inaccurate to suggest the regime has fully tested, developed or demonstrated the kinds of nuclear capabilities referenced”.

The North has conducted three nuclear tests, but it was not believed to be near weapons capability.

South Korea is in a state of high alert after the North, claiming the US is planning to invade, threatened nuclear war. China has carried out a civilian emergency drill and evacuation in a town near its border with the North.