North Korea can mount a nuclear warhead on a medium-range missile, a South Korean official has said, in a new assessment of the capability of a country that conducted its fourth nuclear test this year.
North Korean leader Kim Jong Un said last month his country had miniaturised nuclear warheads to mount on ballistic missiles.
It was his first direct statement of a claim often made in state media though never independently verified.
"We believe they have accomplished miniaturisation of a nuclear warhead to mount it on a Rodong missile," the South Korean official, with knowledge of South Korea's assessment of the North's nuclear program, told a small group of reporters on condition of anonymity on Tuesday (local time).
The Rodong missile can fire a one-tonne warhead a distance of up to 2000km, the official said.
That would put all of South Korea, most of Japan and parts of Russia and China in range.
"We believe they have the ability to mount a nuclear warhead on a Rodong. Whether they will fire it like that is a political decision," the official said.
There was no direct evidence that the North has successfully mounted a warhead on such a missile, he said.
He declined to discuss the basis for the change in assessment.
The South's conservative president, Park Geun-hye, has reversed a policy of trying to engage the North in dialogue, instead adopting a hard line against it, particularly since the North conducted its fourth nuclear test in January and a month later launched a long-range rocket putting an object into space orbit.
The test and launch prompted the UN Security Council to impose new sanctions.
South Korea has previously said North Korea had made progress in its efforts to miniaturise a nuclear warhead, but the capability was incomplete.
South Korea's Defence Ministry said on Tuesday that assessment remained the military's position.