The United Nations on Monday said the 1953 truce agreement that ended Korean War armed hostilities still holds regardless of North Korea's assertion it is was no longer bound by the measure, Kyodo News reported.
"This armistice agreement is still valid and still in force," U.N. Secretary General Ban Ki-moon's spokesman Martin Nesirky said to journalists. The accord does not permit nations "unilaterally to free themselves from it," he said.
Pyongyang must "continue to respect the terms of the armistice agreement as it was approved by the General Assembly," Nesirky said.
The Stalinist state's assertion that the armistice is dead comes after the North was punished with new sanctions last week by the U.N. Security Council as a consequence for its Feb. 12 nuclear test.
South Korea is worried North Korea is laying the groundwork for justifying a possible military strike, the Wall Street Journal reported.
U.S. national security advisor Tom Donilon in a Monday speech said "the days when North Korea could exploit any seams between [Japan, South Korea and the United States] are over."
Donilon also played down North Korea's threat last week that it would launch a pre-emptive ICBM strike on the United States. Pyongyang is widely judged to not yet have developed a reliable nuclear-armed strategic missile that could target the U.S. mainland.
The United States "will draw upon the full range of our capabilities to protect against, and to respond to, the threat posed to us and our allies," he said in an address to the Asia Society.
An unidentified senior South Korean government official told the South Korean JoongAng Ilbo newspaper that U.S. nuclear-armed submarines will remain close to South Korea as part of the extended deterrence Washington provides to its longtime ally against North Korean threats, Kyodo reported.
Issue specialists are watching for a new North Korean provocation similar to its suspected 2010 sinking of a South Korean warship or its acknowledged shelling of the South's Yeonpyeong Island later that year, the Associated Press reported. Seoul has vowed to respond with force to any such attack.
The Obama administration has moved quickly to implement the latest round of U.N. sanctions against the North. The State Department on Monday added three more people with ties to the nation's arms programs to a domestic blacklist. They are North Korean National Defense Commission Vice Chairman O Kuk Ryul, Munitions Industry Department director Chu Kyu Chang, and Munitions Industry Department head of weapons production and sales Pak To Chun.
The international nuclear testing surveillance organization on Tuesday acknowledged that no radioactive material from the North's nuclear test is likely to be found, Reuters reported.
"It is very unlikely that we will register anything ... at this late stage," said Annika Thunborg, spokeswoman for the Preparatory Commission for the Comprehensive Test Ban Treaty Organization.
The Vienna, Austria-based agency identified seismic movement produced by the detonation. However, the absence of detected radioactive particles leaves open the question of whether the North used a plutonium or uranium device one month ago. It suggests the nation was able to block any radioactive material or noble gases from being vented from the underground test chamber.