Unification Minister Ryoo Kihl-jae told a parliamentary committee Monday that "there is such an indication" of nuclear test preparations at Pyongyang's site in the country's northeast, according to two ministry officials who spoke on condition of anonymity because they were not authorized to speak publicly on the matter.
Either a nuclear test or a missile test would escalate tensions that have been rising for weeks on the Korean Peninsula, and could invite a new round of U.N. Security Council sanctions over North Korea's nuclear and rocket activity. The U.S. and South Korea have been raising their defense posture, and foreign diplomats were considering a warning from Pyongyang that their safety in North Korea could not be guaranteed beginning Wednesday.
North Korea has unleashed a flurry of war threats and provocations over the U.N. sanctions and ongoing U.S.-South Korean military drills, which the allies say are routine but Pyongyang says is a preparation for a northward invasion.
Ryoo made his comment in answering a lawmaker's question about increased personnel and vehicle activities at the North's nuclear test site.
Ministry officials cite Ryoo as telling the lawmakers he wouldn't provide further details because they involve confidential intelligence affairs.
South Korean defense officials previously said the North completed preparations for a nuclear test at two underground tunnels. The North used one tunnel for its Feb. 12 nuclear test. The second remains unused.