The missile is currently estimated to have a range of 4,000-5,000 miles – enough to reach Alaska or Hawaii, according to aerospace engineer John Schilling.
He said: “If the Hwasong-14 is put together the way we think it is, it can probably do a bit better than that when all the bugs are worked out.”
Speaking to 38 North – a monitoring project linked to Johns Hopkins University in Baltimore, USA – Schilling warned the rocket is “likely” to be able to deliver a half-tonne warhead to San Diego within two years.
Schilling added: “The North Koreans won’t be able to achieve this performance tomorrow, but they likely will eventually.”
At present it would be “lucky to hit even a city-sized target”, due to limits to its re-entry technology, he said.
But with “a year or two of additional testing and development”, he added, “it will likely become a missile that can reliably deliver a single nuclear warhead to targets along the US west coast, possibly with enough accuracy to destroy soft military targets like naval bases”, such as that at San Diego in California.
The North’s missile technology – which it is banned from developing by the UN Security Council – has advanced rapidly under Kim, ramping up tensions between Pyongyang and Washington.
The impoverished state has also staged five nuclear tests – including two last year.
Washington is set to to propose tougher UN sanctions against the North, but analysts say they will have a limited impact unless China – the North's only major ally – steps up pressure.
Beijing is reluctant to risk destabilising the North, fearing a potential influx of refugees along the frontier or US troops stationed on its border in a unified Korea.
