North Korea has sparked increased fears of a missile attack or new world war after carrying out its most powerful nuclear test ever.
Experts worry the secretive country could eventually develop a long-range missile tipped with a nuclear warhead capable of hitting countries as far away as the US or UK.
Kim Jong-un has recently test-fired two Hwasong-14 intercontinental ballistic missiles (ICBM), in addition to the purported hydrogen bomb test which caused a major earthquake at the weekend.
The missile has an estimated range of more than 10,000 km (6,210 miles), putting London within striking distance and New York and Washington nearly within reach.
North Korea tested its first Hwasong-14 missile on July 4 and followed it up with more successful test on July 28, with the projectile flying 1,000 km (620 miles) before crashing into the sea.
South Korean officials believe that a third ICBM test could take place as early as this weekend.
The Hwasong-14 is the longest range ballistic missile North Korea has ever tested and is the first ICBM it has flown, according to the CSIS Missile Defense Project.
Based on the July 28 test, it has an estimated range of more than 10,000 km, making it capable of reaching most of the continental US.
Maps drawn by experts have also put the UK within that range.
Last week, Japanese Prime Minister Shinzo Abe warned that North Korean missiles could reach Europe.
Speaking after the North fired a missile over Japan, he said: “That threat is felt not only by our country or Asia alone, it has become a global threat, including (to) Europe.
“North Korea will launch ICBM and the range would include almost the entire region of Europe.”
What remains to be seen is whether North Korea can develop a reliable ICBM and nuclear bomb small enough to fit inside the tip.
South Korean Defence Minister Song Young-moo revealed on Monday that North Korea had succeeded in reducing the size and weight of its nuclear warhead.
Kim Jong-un’s regime claimed on Sunday that it had tested a hydrogen bomb and that it was a “complete success”.
South Korean spies believe the North is planning to fire another missile, possibly an ICBM, and the launch could take place on or around Saturday.
In response to the nuclear test, South Korea carried out live-fire missile drills and the US could move an aircraft carrier and bomber jets to the region.