What are intercontinental ballistic missiles, what speed do ICBMs travel at, what is their range and what are they used for?
KIM Jong-un, North Korea's war-hungry ruler has dramatically ramped up his country's ballistic missiles programme since he took power.
Here's all you need to know about the long-range versions of these rockets which are capable of carrying nuclear warheads.
What is an intercontinental ballistic missile?
It is a guided ballistic missile - which follows a path - and has a range of 5,500kms.
They are primarily designed for nuclear weapons delivery but can also carry chemical and biological weapons.
They were first developed in World War Two.
In 1943 US Army General Hap Arnold wrote: "Someday, not too distant, there can come streaking out of somewhere - we won't be able to hear it, it will come so fast - some kind of gadget with an explosive so powerful that on projectile will be able to wipe out completely this city of Washington."
These missiles can carry a number of separate nuclear warheads - which means a single missile can hit multiple targets.
After North Korea launched missiles over the Japanese border on August 29, 2917, South Korean residents were then urged to take immediate shelter underground as four F-15K fighter jets dropped eight MK-84 bombs on targets at a military field near the border.
On November 28, 2017, North Korea launched ICBM Hwasong-15 – which is a new nuclear missile capable of hitting anywhere on the planet.
Pyongyang said the mega-missile then reached an altitude of around 2,780 miles - more than ten times the height of the international space station - and flew 600 miles during its 53-minute flight.
But one physicist said the missile appeared to have a realistic attack range of just over 8,000 miles, which means Washington DC is now in range - along with Australia and Europe.
In March 2018, Vladimir Putin announced Russia had developed a new ICBM which was invulnerable to enemy missile defence systems.
What speed do the missiles travel at?
An intercontinental ballistic missile constantly changes speed and altitude.
But the peak speed of an ICBM is about 6-7km/s.
New York to Moscow is 7,500 and at 6.5km/s would take about 20 minutes for a missile to reach there.
MOST READ IN WORLD NEWS
What are they used for?
ICBM's have a greater range and speed than other ballistic missiles.
They were initially intended to be used to bomb American cities by the Nazis.
In the Cold War, the US and USSR started rocket research programs based on the German designs.
And these early prototypes formed the basis of many of the space launch systems.
As of 2016 all five of the nations with permanent seats on the United Nations Security Council - China, Russia, the US, Great Britain and France - have operational long-range ballistic missile systems.
North Korea mounted tensions by launching a missile over Japan in August 2017 - in what was thought to have been another threat against US territory Guam.
Officials said it was the first time the communist state has fired a mid-range ballistic missile designed to carry a nuclear payload over Japan before it splashed into the northern Pacific Ocean.