South Korean says North Korea has developed the technology to fire a missile about 10,0000, which would theoretically put parts of the western United States within range.
The estimate is based on an initial analysis of rocket debris. The defence ministry said debris from the second and third stages of a recent rocket launch is still to be analysed.
However, there is no confirmation that the North has the re-entry technology needed to deliver a missile.
Experts believe North Korea is also years away from gaining the ability to mount a nuclear bomb on a missile.
North Korea launched a three-stage rocket to put a satellite into orbit on 12 December, in defiance of international sanctions.
The BBC reports North Korea insists it's rocket programme is part of a civilian space programme.
