Mr Lewis said: “North Korea almost certainly has a compact fission warhead capable of fitting on a future ICBM.
“The major question now is notwhether the warhead is small enough to mount on an ICBMbut whether it is rugged enough to survive the shock, vibration and extreme temperatures that a nuclear warhead would experience on an intercontinental trajectory, in which it would be shot into space and then re-enter the Earth’s atmosphere.
“The warhead fitted to the Hwasong-12 experienced heat loads similar to those of an ICBM (although for a shorter period of time) and survived.
“Separately, North Korea has published images of an apparently successful ground test of a re-entry vehicle last year.”
In recent months, North Korea has rapidly stepped up its missile launch programme.
Four new weapons systems have been tested lately, including new super-accurate short-range ballistic missiles.
Its new intermediate-range ballistic missile are said to be able to hit US bases in Guam and NK has also tested new anti-ship cruise missiles.
And Mr Lewis fears the rogue state could soon be “knocking on the door” of the US with new super-powered ICBMs – despite some claiming Kim’s missile programme is overrated. READ MORE