North Korea missiles
Image from North Korean television shows a rocket being fired in military exercises. (Getty) Getty

A US research has institute predicted that North Korea could build as many as 100 nuclear weapons in the next five years.

The US special representative for North Korea Policy, Sung Kim, said that the US government was "deeply concerned" about North Korea's growing nuclear might, following the report by the US -Korea Institute at Johns Hopkins University's School of Advanced International Studies.

"Obviously we are deeply concerned about the fact that the North Koreans are continuing to advance their nuclear capabilities; we know that they are continuing to work on their nuclear program," Kim told Reuters.

The report describes a "worst case scenario" in which Kim Jong-Un's despotic government is able to build 100 nuclear warheads by 2020, with the country's current nuclear stockpile believed to consist in about 16 nuclear missiles.

According to the report, Pyong yang has succeeded in miniaturising nuclear warheads, allowing them to be fitted to ballistic missiles.

"This is a pretty scary scenario," report author Joel Wit said, adding that the more its nuclear arsenal grew, the more difficult it would be to persuade Pyonyang to roll back its nuclear programme.

"To me it's a risky business trying to punish a country with so many nuclear weapons."

The report added that North Korean missiles currently had the capacity to reach South Korea and Japan, and it was developing the taepodong 2 model capable of striking the US.

It warned the international community to take steps to tackle the growing danger, and said that as North Korea's nuclear know-how grows, it will be in a position to export its expertise to other countries.

Kim said Washington would "continue to apply pressure both multilaterally and unilaterally" though sanctions to increase the cost of North Korea failing to voluntarily de-nuclearise.