A TOP expert has claimed North Korea’s military is just one step away from launching a nuclear–tipped intercontinental ballistic missile capable of reaching the US.

Jeffrey Lewis, an American expert on Kim's Jong-un's military, believes the only hurdle left is to develop a warhead capable of handling the extreme heat encountered during re-entry into our atmosphere.

7 A photograph of a test-fire of an ICBM released by the North Korean military Credit: EPA

7 North Korean leader Kim Jong-un reacts after doing a test-fire of new cruise missile Credit: Reuters

Mr Lewis said: “North Korea almost certainly has a compact fission warhead capable of fitting on a future ICBM.

“The major question now is not whether the warhead is small enough to mount on an ICBM but 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.

7 State video still of Kim in front of a missile launcher in North Korea Credit: AP:Associated Press

7 This photo shows the test fire of a new-type of ground-to-sea cruise rocket Credit: EPA

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.

Mr Lewis added: “Similar doubts were expressed about China's nuclear warheads in the 1960s, prompting China's leaders to arm a missile with a live nuclear weapon and launch it across the country to dispel any lingering doubts. Fortunately, North Korea has not chosen to take such a step.”

Last week, NK today said it "fully rejects" the latest UN sanctions against its citizens as a "hostile act" and will continue its nuclear weapons development without delay.

The UN Security Council on Friday expanded targeted sanctions against Kim Jong-un's rogue state after its repeated missile tests - the first such resolution since President Donald Trump took office.

7 Kim Jong-un has vowed to carry on developing his nukes Credit: Reuters

7 The US missile defence system tested in California can blast rockets out of the sky Credit: EPA

The sanctions resolution "is a crafty hostile act with the purpose of putting a curb on the DPRK's buildup of nuclear forces, disarming it and causing economic suffocation to it," NK's foreign ministry spokesman said in a statement.

"Whatever sanctions and pressure may follow, we will not flinch from the road to build up nuclear forces which was chosen to defend the sovereignty of the country and the rights to national existence and will move forward towards the final victory."

North Korea has rejected all UN Security Council resolutions dating back to 2006 when it conducted its first nuclear test, saying such moves directly infringe its sovereign right to self defence.