The dictator is said to have sent experts around the world to get degrees in microbiology and stepped up moves to build more factories and laboratories. 

And leader of the hermit nation has steadily been acquiring new machinery that could be used to churn out deadly microbes, US and Asian intelligence officials have claimed.

US analysts are concerned the research could mean the regime is producing dangerous microbes and pathogens that could be loaded into bioweapons.

A US official told the Washington Post: “That the North Koreans have biological agents is known, by various means. The lingering question is, why have they acquired the materials and developed the science, but not yet produced weapons?

“If it started tomorrow we might not know it, unless we're lucky enough to have an informant who happens to be in just the right place.”

Although they cannot heavily damage infrastructure, biological weapons can carry lethal viruses like smallpox and anthrax.

Bioweapons may be capable of killing hundreds of people and cause pandemics. 

Their unpredictability means many countries have agreed to ban biological weapons, and 196 countries have signed the Biological Weapons Convention outlawing them.

The claims come as the US, South Korea and Japan start joint exercises to track missiles from North Korea.

The allies are responding the growing tensions in the region as North Korea continues its fast-developing weapons programmes.

And these fresh exercises are the sixth drills sharing information in tracking ballistic missiles among the three allies on Kim Jong-un’s doorstep, according to Japanese officials.

It was not established whether the US’s Terminal High Altitude Area Defence system would be involved in the preparations for further North Korea missile launches.

Kim Jong-un issued a stern warning by Donald Trump as the US began the drills, saying the last large-scale military drills made the outbreak of World War 3 “an established fact”.

On Sunday, South Korea said it will impose new unilateral sanctions on 20 institutions and around a dozen individuals in North Korea.

South Korea’s Finance Ministry said: “This unilateral sanctions will prevent illegal funds flowing to North Korea and contribute to reinforce international communities’ sanctions against North Korea.”

The move is seen largely as symbolic but since Kim Jong-un ramped his threats up against Donald Trump, the US President has seriously bolstered his military might in the region.

Around 28,500 US troops are stationed in South Korea, a legacy of the Korean War between 1950-53.