- Trump-Kim summit
image source, KCNA
North Korea has made rapid progress in its weapons programme, which it claims is necessary to defend itself against a possible US invasion.
Pyongyang started 2021 off with a bang, unveiling what state media has described as "the world's most powerful weapon".
The new submarine-launched ballistic missile was launched at a parade overseen by leader Kim Jong-un – just days before the inauguration of US President Joe Biden.
The weapon's actual capabilities remain unclear, as it is not known to have been tested.
Mr Kim has also pledged to expand North Korea's nuclear arsenal and military potential, outlining a list of desired weapons.
Here's what we know about North Korea's missile and nuclear programme and its military forces.
Missiles that can reach the US
Throughout 2017, North Korea tested several missiles demonstrating the rapid advances of its military technology.
The Hwasong-12 was thought to be able to reach as far as 4,500km (2,800 miles), putting US military bases on the Pacific island of Guam well within striking distance.
Later, the Hwasong-14 demonstrated even greater potential, with some studies suggesting it could travel as far as 10,000km if fired on a maximum trajectory.
This would have given Pyongyang its first truly intercontinental ballistic missile, capable of reaching New York.
Eventually, the Hwasong-15 was tested, peaking at an estimated altitude of 4,500km – 10 times higher than the International Space Station.
If fired on a more conventional "flatter" trajectory, the missile could have a maximum range of some 13,000km, putting all of the continental US in range.
In October 2020, North Korea unveiled its new ballistic missile.
image source, Getty Imagesimage captionA number of large missiles were displayed at North Korea's recent military parade, October 2020
It has not yet been named or tested. Like the Hwasong-15, it is a two-stage liquid fuelled missile, but with a greater length and diameter. It could possibly allow for multiple warheads.
The colossal weapon is is believed to be able to deliver a nuclear warhead to anywhere in the US, and its size had surprised even seasoned analysts when it was put on show last year.
Just months later, in January 2021, North Korea unveiled a new type of submarine-launched ballistic missile at a military showcase, which it declared to be "the world's most powerful weapon".
image source, KCNAimage captionThe missile was debuted at a military parade which came at the end of an important and rare political meeting
The unveiling of the new missiles appeared to be a message to the Biden administration of the North's growing military prowess, say experts.
Then in March, it carried out a launch of what it called a "new-type tactical guided projectile".
North Korea said the new missile was able to carry a payload of 2.5 tons, which would make it capable of carrying a nuclear warhead.
The weapon has not been formally identified but analysts at the James Martin Centre for Nonproliferation Studies told Reuters that it appeared to be "an improved variant" of a previously tested missile, the KN-23.
Mr Kim had earlier declared that the US was its "biggest enemy", as he outlined a list of desired weapons including long-range ballistic missiles capable of being launched from land or sea and "super-large warheads".
- North Korea unveils new submarine-launched missile
- Kim vows to expand North Korea's nuclear arsenal
North Korea has managed to significantly advance its arsenal despite being subject to strict economic sanctions.
On 3 September 2017 North Korea conducted by far its largest nuclear test to date, at its Punggye-ri test site.
Estimates of the device's explosive power, or yield, ranged from 100-370 kilotons. A yield of 100 kilotons would make the test six times more powerful than the bomb dropped on Hiroshima in 1945.
North Korea claimed this test was its first thermonuclear weapon – the most potent form of nuclear explosion where an atomic detonation is boosted by a secondary fusion process to produce a far bigger blast.
American military intelligence believes that North Korea has successfully miniaturised a nuclear warhead to fit inside a missile.
In April 2018 North Korea announced it would suspend further nuclear tests because its capabilities had been "verified".
media captionIs North Korea's nuclear site destruction for real?
North Korea then also promised to dismantle the Punggye-ri site and in May blew up some of the tunnels in the presence of foreign journalists but with no international experts .
Pyongyang also said then that it would destroy all its nuclear material enrichment facilities.
Millions of soldiers
North Korea has one of the largest standing armies in the world – with more than one million soldiers and estimated reserves of some five million.
Much of its equipment is old and obsolete, but its conventional forces could still inflict massive damage on South Korea in the event of war.
North Korea also has around 200,000 special forces troops which could be expected to infiltrate the South in the event of any conflict.
They could potentially exploit a semi-secret network of 20-25 large tunnels which span the Demilitarized Zone (DMZ) – the border area – emerging behind South Korean and American forward lines.
A further threat comes from thousands of North Korean artillery pieces and rocket launchers deployed along the border. Their firepower could devastate South Korea, including the capital Seoul, which at a distance of less than 60km, is well within range.
Chemical weapons could also be used. In 2012 the South Korean government assessed that North Korea could have between 2,500 and 5,000 tons of chemical weapons, potentially one of the largest stockpiles on Earth.
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- What have North Korea's nuclear tests achieved?
American forces in South Korea and the wider region
The United States has had a military presence on the Korean Peninsula since the Korean War.
Today, South Korea has the third highest deployment of US troops anywhere in the world with around 28,500 troops stationed across the country.
image source, Getty Imagesimage captionUS strategic bombers have carried out training flights over the Korean peninsula.
Washington has also installed its controversial THAAD missile defence system in South Korea, which would be used shoot down North Korean short and medium range missiles in the event of war.
In the wider region, Japan hosts more US forces than any other nation with some 50,000 deployed, the majority being naval personnel. It also has an aircraft carrier based in Japan.
There are also significant US forces on the US Pacific island of Guam, which is sometimes described as a "permanent aircraft carrier".
North Korea has previously threatened to fire missiles at the waters around Guam.