The Nuclear Safety and Security Commission said its land-based xenon detector in the northeastern part of the country found traces of xenon-133 isotope on nine occasions, while its mobile equipment off the country's east coast detected traces of the isotope four times.
Tensions over a raft of provocations by North Korea are not high enough to adjust ratings on South Korea, a senior official of the global rating agency Standard & Poor's said Thursday.
Pyongyang was punished through oil trade restrictions among other measures adopted by the United Nations Security Council after the North's most powerful nuke test to date on September 3.
Just days before his departure to New York City, President Moon Jae-in squashed the idea of South Korea's self-nuclear armament amid North Korea's recent missile launches and nuclear test.
The administration of U.S. President Donald Trump is considering unilateral sanctions against Chinese trading companies engaged in crude oil trade with North Korea, according to sources close to the U.S. government.
It added: 'Let's vent our spite with mobilisation of all retaliation means which have been prepared till now.
Moon said he believed North Korea wanted to ensure "regime stability" and to be accepted as a nuclear power state, with a seat at the negotiating table with the US.
North Korea says it needs nuclear weapons to protect itself from "hostile" U.S. forces. Let's reduce the U.S. mainland into ashes and darkness.
However, Seoul's Unification Ministry revealed Thursday that the government is mulling over whether to provide the North with $8 million in aid despite sanctions.
The North's latest threats also singled out Japan for "dancing to the tune" of the United States, saying it should never be pardoned for not offering a honest apology for its "never-to-be-condoned crimes against our people", an apparent reference to Japan's wartime aggression.
Tokyo blasted the North Korean statement as "extremely provocative and egregious".
Japanese Prime Minister Shinzo Abe, visiting India, called for strict enforcement of the United Nations resolution, saying the world must force a change.
The United States demanded that the UN impose the strongest possible sanctions on North Korea, including cutting off the country's oil supply completely. Although the latest sanctions are not as tough as what the US had sought, they are expected to have a significant impact.
The latest sanctions also make it illegal for foreign firms to form commercial joint ventures with North Korean entities.