Last Friday, the mood for cross-border ties appeared fairly upbeat as North Korean leader Kim Jong-un expressed his resolve for dialogue instead of touching on his nuclear ambitions in his New Year’s address, which was duly noted by President Park Geun-hye who responded positively.

Less than a week later, the situation has reversed. Pyongyang declared it successfully carried out a hydrogen bomb test Wednesday, catching everyone off guard ― not just Seoul and Washington, but also Beijing, the communist country’s top political and economic patron.

The fourth test marks the latest in a series of dogmatic and perplexing behavior by the young leader. 

The state media said the decision was made by Kim, who signed the order on Dec. 15, shortly after the Moranbong Band canceled a much-hyped sold-out concert in Beijing at the last minute without giving a reason, sparking international criticism and extensive rumors.

Military officials here have said the North is ready to conduct nuclear tests at any time once it takes such a “political choice,” and related evidence can be detected up to one month ahead. But this time, there were no imminent signs of a test ― such as setting up a measuring device and screen fence or refilling the tunnel ― indicating the preparations were made in a highly clandestine manner.

Covert preparations aside, the timing was unusual, defying the longstanding pattern of a long-range missile test leading to international sanctions followed by a new atomic test.

Pyongyang’s provocations are chiefly aimed at nuclear talks with the U.S., and have in the past come at times of leadership transition or major political events. This time, however, it did not have much incentive, given that the Barack Obama administration has displayed little, if any, willingness to forsake its “strategic patience” approach and return to disarmament-for-aid negotiations, and the presidential election isn’t scheduled until November.

On the cross-border front, the latest test will inevitably complicate Seoul’s calculations over Pyongyang’s demand for a restart of stalled tours to a North Korean mountain resort and lifting of bans on bilateral exchanges.

With Kim’s birthday falling on Friday, the test could have been designed to elevate the occasion as a new major anniversary alongside those of his deceased father and grandfather, while consolidating the ruler’s legacy ahead of the ruling Workers’ Party’s first congress in 36 years slated for May, some observers say.

They also called for the Park Geun-hye administration to refine its North Korea approach instead of shifting all the blame to the unpredictable leader, citing Kim’s claim last month of having developed a hydrogen bomb, which Seoul dismissed as a “rhetoric.”

“Though Kim is mocked globally, I’m not sure if he is controlling the entire situation under a thoroughly crafted scenario, and when everyone undermines his remarks as a bluff, he strikes back with a surprising provocation contrary to widespread expectations,” a Seoul official said on customary condition of anonymity.

By Shin Hyon-hee (heeshin@heraldcorp.com)