Pyongyang has previously fired missiles capable of reaching the entire US mainland, and has carried out six nuclear tests, the last of them 16 times more powerful than the Hiroshima blast, according to the highest estimates. A self-imposed ban on such tests - Kim declared they were no longer needed - has been a centrepiece of the nuclear diplomacy between Pyongyang and Washington over the past two years, which has seen three meetings between Kim and the US president, but little tangible progress.
Any actual test is likely to infuriate Trump, who has repeatedly referred to Kim's "promise" to him not to carry them out, and has downplayed launches of shorter-range weapons. Negotiations between the two sides have been largely deadlocked since the breakup of their Hanoi summit in February. The North set the US an end-of-2019 deadline for it to offer fresh concessions on sanctions relief, or it would adopt a "new way".