North Korea's missile programme
North Korea's missile arsenal has progressed over the decades from crude artillery rockets derived from World War II designs, to medium-range missiles able to strike targets in the Pacific Ocean.
The push for a long range missile
North Korea's latest efforts appear focused on building reliable long-range missiles, which may have the potential to reach the mainland United States.
Two types of intercontinental ballistic missile (ICBM) known as the KN-08 and KN-14, have been observed at various military parades since 2012.
Carried and launched from the back of a modified truck, the three-stage KN-08 is believed to have a range of about 11,500km.
The KN-14 appears to be a two-stage missile, with a possible range of around 10,000km.
Neither missile has yet been flight tested, but recent images have shown engine trials under way and what appears to be a heat shield for a warhead being tested.
Despite this apparent progress, North Korea is still thought to lack the ability to accurately target a city with an ICBM, or miniaturise a nuclear warhead.
Why build ICBMs?
Intercontinental ballistic missiles are seen as the last word in power projection because they allow a country to wield massive firepower against an opponent on the other side of the planet.
The only real reason to spend the money, time and effort building them is to fire nuclear weapons.
During the Cold War, Russia and the United States sought different ways to protect and deliver their missiles, which were hidden in silos, piggybacked on huge trucks or carried by submarines.
All ICBMs are designed along similar lines. They are multi-stage rockets powered by solid or liquid fuel, and carry their weapon payload out of the atmosphere into space.
The weapon payload - usually a thermonuclear bomb - then re-enters the atmosphere and detonates either above or directly on top of its target.
Some ICBMs have a "multiple independently targetable reentry vehicle", or Mirv.
This has multiple warheads and decoys to allowing it to strike multiple targets and confuse missile defence systems.
In the Cold War period, the range and potential threat of ICBMs were seen as key to the concept of "Mutually Assured Destruction" or MAD.
MAD supposedly helped maintain peace because neither side could "win" without suffering incalculable damage.
The North's missile milestones
North Korea's own missile programme began with Scuds, with its first batch reportedly coming via Egypt in 1976.
By 1984 it was building its own versions called Hwasongs.
These missiles have an estimated maximum range of about 1,000km, and carry conventional, chemical and possibly biological warheads.
From the Hwasong came the Nodong design - effectively an upscaled Hwasong / Scud with a extended range of 1,300km.
In an April 2016 analysis, the International Institute for Strategic Studies said the missiles were a "proven system which can hit all of South Korea and much of Japan".
More capable missiles followed with the development of the Musudan range, which was most recently tested in 2016.
Estimates differ dramatically on its how far it can fly, with Israeli intelligence putting it at 2,500km and the US Missile Defense Agency estimating about 3,200km. Other sources suggest a possible 4,000km.
Another development came in August 2016 when North Korea announced it had tested a submarine based "surface-to-surface, medium-to-long-range ballistic missile", called the Pukguksong.
A second was launched from land in February 2017.