What lies behind North Korea's nuclear claims
Official claims by North Korea that it has successfully developed the technology to "miniaturise" a nuclear device and, by implication, deploy it on a ballistic missile, have raised international concerns about the growing security threat posed by North Korea to its neighbours.
This, together with the apparent test firing by the North on 8 May of a submarine-launched ballistic missile, and reports last month of the possible execution of Defence Minister Hyon Yong-chol, suggest that the country is intentionally pursuing a more explicitly confrontational and aggressive foreign and domestic policy.
High-profile military initiatives, allied with the purge of senior members of the North Korean elite, suggest that Kim Jong-un, the country's inexperienced 32-year-old leader, may be seeking to strengthen his authority at home.
By removing his political rivals, bolstering his credentials as the country's top military leader, and fostering a sense of crisis with the outside world, he may be trying to rally the domestic elite and mass opinion ever closer around his leadership.
Since assuming power following the death of his father Kim Jong-il in December 2011, Kim Jong-un has moved deliberately, often brutally, to remove from positions of influence individuals associated with the previous government.
The clearest illustration of this trend was the swift and very public trial and execution in January 2013 of Chang Song-thaek, Kim's uncle and (until his abrupt fall from grace) one of the country's most senior and influential officials, reportedly hand picked by Kim Jong-il to act as mentor and regent to the new leader.
Vice-Marshal Hyon's unexpected demise appears to bear similar hallmarks and comes in the wake of the purge of 15 senior officials over the last year.
While the precise circumstances surrounding Hyon's removal remain unclear, he appears to have been punished for insubordination and possibly also for failing to secure an agreement with Russia to provide the North with conventional surface-to-air missile batteries.
The continuing purge of senior military and party officials demonstrates the concentration of political power in North Korea and the absence of any obvious counterweights to Kim's authority.
Equally it may be a sign of Kim's growing isolation and possible weakness in the face of wider public discontent - fuelled by persistent economic hardship - and of diminishing central control over the Korean populace.
It is too early to say where the balance lies between these two views, but Kim's increased use of fear as a means of asserting control, even over those closest to the leader, hints at emerging cracks in the authority and legitimacy of his rule.
Keeping North Korea militarily secure allows Mr Kim to demonstrate his success as the country's commander-in-chief and his very public presence at the 8 May submarine missile launch was a characteristically calculated effort to reinforce his military credentials.
Although some have questioned the veracity of the photographs of the launch, the test represents a significant step forward in the North's long-term plan to develop its sea-based launch capabilities (a departure from its traditional reliance on land-based delivery systems), but one which is still probably some two years away from deployment as an actual working submarine-launched ballistic missile system.
Where miniaturisation is concerned, technical opinion still remains divided. As recently as this April, Admiral William Gortney, head of the United States' Northern Command, publicly stated that North Korea is able, in principle, to deploy a nuclear device on the North's new KN-08 missile, but is yet to test its technology in this regard.
South Korean views are more circumspect, but there is little doubt that it is probably only a matter of a few years before the North is successful in marrying its nuclear and increasingly sophisticated ballistic missile capabilities to allow it to launch a nuclear strike at Seoul, and perhaps as far afield as Tokyo and the West Coast of the United States.
For both the US and South Korea, under President Park Geun-hye, there are few immediately attractive solutions to these new provocations from the North.
Bilateral relations between Seoul and Pyongyang are at a low ebb, dominated by harsh rhetoric on both sides, and, in the case of the North's approach, insulting, ad hominem propaganda directed against Ms Park.
Pyongyang's abrupt cancellation of a planned visit by UN Secretary General Ban Ki-moon to the Kaesong Industrial Complex, the North's flagship special economic zone, suggests that there is little immediate room for fruitful high-level international dialogue.
By default, therefore, strengthening deterrence is the most obvious way forward and this is likely to be a subject of discussion at next month's summit between Ms Park and President Barack Obama in Washington.
It is also likely to have implications for the continuing debate between the US and South Korea over the planned deployment of US anti-missile defence technology on the peninsula - the so-called THAAD, or Terminal High Altitude Area Defence system.
Washington is keen to encourage THAAD, but many in Seoul are concerned that it might antagonise China and also signal a weakening in South Korea's defence autonomy.
Alongside deterrence, the US and its allies can continue to rely on international economic sanctions, but these have had little effect in materially retarding the North's military program, not least because China remains reluctant to impose meaningful pain on North Korea for fear of provoking more instability on the peninsula.
At best, we are likely to see more public international condemnation of the North's provocations and perhaps, as US Secretary of State John Kerry has recently hinted, a reporting of the North to the International Criminal Court in the face of its worsening human rights record.
The current impasse remains a worrying sign of growing insecurity in Northeast Asia and of North Korea's ability to use its very vulnerability, and the limited policy options of its opponents, to play for time while incrementally enhancing its military capabilities with relative impunity.
John Swenson-Wright is head of the Asia programme at Chatham House