North Korea once again demonstrated its mastery of timing and exposed the limits of any international response as it caught the world off-guard with its surprise nuclear test.

The detonation angered its traditional ally China as well as earning denunciations from historic rivals elsewhere in Asia and in the United States and Europe.

The event may have been billed as an early present for Kim Jong Un, the North Korean leader, who celebrates his birthday today. But it will not have been his personal calendar that determined the timing.

For all the condemnation it is facing, Pyongyang carefully unleashed its latest show of nuclear muscle at a time when minds elsewhere are focused on other international crises.


Kim, a young leader still keen to signal his grasp on power, will also have been looking towards his domestic audience ahead of what is expected to be the first party congress in 35 years in May.

"Advancement of North Korea's nuclear programme is a pillar of Kim's legitimacy," said Yanmei Xie, an Asia analyst with the International Crisis Group. "It is inconceivable to see Kim reverse this track unless he can be convinced that failure to denuclearise jeopardises the survival of his regime." And so his regime has forged ahead with its fourth nuclear test, apparently confident that its survival will not be endangered.

In Europe, governments are focused on the refugee crisis and events in the Middle East, particularly given the escalating crisis between Saudi Arabia and Iran.

Pyongyang may well have calculated that Barack Obama is entering his final year as US President seeking legacy achievements and will have little appetite for a fresh confrontation with North Korea as he continues to struggle with the hangover of American conflicts in Iraq and Afghanistan.

But most crucial to Pyongyang is the reaction of China, the one country that could pull the plug on the regime by ending its financial support.

The Chinese Foreign Ministry spokesman made it clear at the daily briefing that Beijing had no advance warning of the test.

Beijing is also concerned about unrest at home over the uncertain economic situation and will shy away from any course of action that might provoke domestic disquiet, analysts in the region believe.

If China has a greater fear than North Korea's growing nuclear capability, it is the ramifications of the country's collapse.


And as Xie noted, if China has a greater fear than North Korea's growing nuclear capability, it is the ramifications of the country's collapse.

"China keeps the Kim regime afloat with fuel supply, food assistance, and an opening out of diplomatic and economic isolation. It is difficult to imagine that China is ready to abandon Kim even after another nuclear test, even though the relations will experience a deepening chill," she said.

"For Beijing, a nuclear armed North Korea is uncomfortable and disturbing, but a regime collapse in Pyongyang exposes China to mass chaos next door and a potentially united Korean Peninsula. This could extend Washington's influence northward to China's doorstep, a situation that is outright frightening for Beijing."

Toshimitsu Shigemura, a professor at Tokyo's Waseda University and an authority on the North Korean leadership, said that he believed North Korea was looking at a three-month time frame to improve relations with Beijing.

"I believe that by carrying out the test now, Mr Kim has three months to soothe relations with China, which is still his most important ally," he said.

"North Korea has announced that it will hold its first party congress in 35 years in May and Mr Kim may not feel that he has done enough to cement his position, so showing that he now has a hydrogen bomb is calculated to significantly boost his standing."

Rah Jong Yil, a former head of South Korean intelligence, expressed doubt that the response would differ significantly from previous crises.

"This has come as a serious shock in South Korea and my sense is that there are no feasible options to stop Pyongyang on this path. The international community will condemn these actions, but we have no effective way of counteracting this development. Even China, which has acted as a stabilising force in the past, does not have so many cards to play."

Shigemura expects Pyongyang to be more conciliatory again as the year progresses.

That would echo the tried-and-tested approach by the regime over several decades that has promised detente and cooperation but served only to buy time for Pyongyang to develop nuclear weapons and the long-range missiles with which to deliver to them.

North Korea may also seek to extract concessions from its enemies in the past, heightening international tensions to then demand aid in return for appearing to back down.

"Mr Kim wants to negotiate from a position of strength and he has been closely watching the resolution of Iran's nuclear situation," Shigemura added.

"And President Obama is entering his final year in office and many previous US leaders have tried to make progress on the Korea question as their terms come to an end. Mr Kim may very well be expecting the President to do something similar and offer talks."