It comes as North Korea has been ramping up its missile technology with regular rocket tests, including two intercontinental ballistic missiles launches and its sixth nuclear bomb detonation earlier this year.
North Korea has also threatened to totally destroy the US and warned Donald Trump “should think twice about what terrible consequences the US will face”.
The US President is set to visit the region next month where he will reportedly inspect American forces at one of the largest bases on the Korean Peninsula.
And now a US Government source has revealed the despotic state secretly tested a new type of solid-fuel engine last week.
According to the source, the test took place at North Korea’s solid-fuel engine testing site in Hamhung.
Solid-fuelled missiles would give North Korea an advantage as they are ready to fire at a moments notice.
North Korea’s arsenal up until now was understood to have relied mainly on liquid-fuelled missiles, which are simpler and cheaper to make but are slower to launch as they can only be loaded at the time of fire.
Earlier this year North Korea unveiled its KN-15 rocket, which is a land-based version of its deadly submarine-launched ballistic missile.
The missile, called the Pukguksong-2 or “Polaris-2”, is powered by solid fuel which would make it almost undetectable by US satellites in the event of war.
Melissa Hanham, a senior researcher at the James Martin Centre for Non-proliferation Studies, told the Washington Post: “Solid fuel is very significant because they can launch these missiles much faster and with a smaller entourage than with liquid-fuelled missiles, making them much harder for the United States, South Korea and Japan to spot from satellites.”
The missile engine test comes as a senior CIA analyst warned that Donald Trump’s visit to China, Japan and South Korea in November could spark another provocation from Kim Jong-un.
Japan’s defence minister has also warned North Korea’s threat has grown to a “critical and imminent level”.
At the time the official added it “had not been decided” if Trump would visit heavily fortified demilitarised zone (DMZ) which separates the north and south.
Since the 1980s, every US president except for George H W Bush has visited the DMZ, which is patrolled by thousands of North Korean troops.
Another White House official said the final details of the South Korean leg of the trip are still being ironed out.
Vice President Mike Pence visited the DMZ earlier this year.