North Korea is showing "signs" of readying for its fourth nuclear test, Agence France-Presse quoted a senior South Korean official as saying on Monday.
Information gleaned from the North indicates an uptick in work at the Punggye-ri complex, site of the North's previous underground atomic blasts, according to Unification Minister Ryoo Kihl-jae.
"We are trying to figure out whether it is a genuine preparation for a nuclear test or just a ploy to heap more pressure on us and the U.S.," an anonymous official in Seoul told the JoongAng Ilbo newspaper.
The South Korean Defense Ministry, though, on Monday said "we found there had been no unusual movements that indicated [North Korea] wanted to carry out a nuclear test," Reuters reported.
Ryoo later said he had spoken incorrectly; a spokeswoman said his meaning was that the North is generally prepared for another test, the Associated Press reported.
Other South Korean officials, though, suggested Pyongyang might in coming days carry out a nuclear test in tandem with a ballistic missile launch, Bloomberg reported.
The North's nuclear test in February led to another round of U.N. Security Council sanctions against the regime. That drew a spate of threats from Pyongyang, which also cut off military communications with Seoul and declared the Korean War armistice null and void. On Monday it halted work with the South at the shared Kaesong industrial complex, Reuters separately reported.
The United States has in the meantime put on a show of force in the region, including flyovers by nuclear-capable B-2 and B-52 bombers. Seoul and Washington have also made preparations for a strong reaction to any North Korean provocation that would aim to avoid sparking a widespread armed conflict, the New York Times reported.
Another nuclear test would be a "provocative measure" that would violate Security Council mandates, U.N. Secretary General said on Monday in an Associated Press article.
North Korea has also reportedly moved two intermediate-range Musudan missiles close to its east coast. A senior South Korean security official on Sunday said another North Korean missile test could be in the offing, the Associated Press reported.
No nation "should be allowed to throw a region and even the whole world into chaos for selfish gain," Chinese President Xi Xinping said over the weekend in a seeming reference to North Korea. Beijing is Pyongyang's last major ally, and so is believed to have some measure of influence over the Kim regime.
"We oppose provocative words and actions from any party in the region and do not allow trouble-making on China's doorstep," Reuters quoted Chinese Foreign Minister Wang Yi as saying.