North Korea refrained from conducting its fourth nuclear test at least during U.S. President Barack Obama’s visit to Seoul last week. Some North Korea watchers here had expected that the isolated communist regime would detonate its latest nuclear device in time for the American leader’s trip.

Last month, Pyongyang threatened to carry out a “new form of nuclear test,” apparently referring to a blast involving an atomic bomb built with highly enriched uranium, which would be a more plentiful weapons-grade fissile material than the plutonium it has been reliant on so far. North Korean officials later warned that “something unimaginable” would take place before April 30, implying that the fourth nuclear test was imminent.

During Obama’s stay in Seoul, however, the North made an unexpected but well-timed announcement that it had been detaining another American citizen for more than two weeks. As Obama wrapped up the first part of a two-day visit here, the North’s official Korean Central News Agency reported Friday that a 24-year-old man named Miller Matthew Todd had been taken into custody on April 10 after he tore up his tourist visa at immigration and demanded asylum. Besides him, a 44-year-old Korean-American man has been detained there since November 2012. The belatedly announced detention of a second U.S. citizen seems to be part of Pyongyang’s continuous but fruitless attempts to open a channel of bilateral dialogue with Washington.

With new satellite images showing heightened activity at the North’s nuclear test site, Obama stood firmly with South Korean President Park Geun-hye in sending a strong warning to the recalcitrant regime. During a joint news conference after their talks Friday, Obama stressed that the U.S. and South Korea “stand shoulder to shoulder both in the face of Pyongyang’s provocations and in our refusal to accept a nuclear North Korea.” In his speech to American troops in Seoul the following day, Obama said Pyongyang’s continued pursuit of nuclear weapons was “a path that leads only to more isolation.”

The South Korean and U.S. leaders also reiterated hope that China would play a greater role in reining in North Korea. Beijing has increasingly toughened its stance against the possibility of an additional nuclear test by Pyongyang, with a Chinese Foreign Ministry spokesman saying Thursday the country would not permit chaos on its doorstep. Recent data compiled by South Korea’s state-run trade agency, which showed China had exported no crude oil to North Korea in the first three months of this year, may be seen as a sign of Beijing’s increasing pressure on its intractable neighbor.

The North Korean leadership should recognize that detonating a fourth nuclear device might be tantamount to suicide as it would trigger more stringent international sanctions that would be hard to endure. But its young ruler, Kim Jong-un, who has built up a reputation for calculated unpredictability, may order another test, believing that it will help enhance the credibility and thus the bargaining power of his nuclear arsenal.

By keeping major neighboring powers in a guessing game, Kim has proven himself to be shrewder and more tactically skillful than he was thought to be when he took power following the death of his father Kim Jong-il in December 2011. But he will ultimately be forced to choose between risking collapse with a nuclear arsenal and trying to survive without it. Survival with nuclear arms will remain beyond his reach.