North Korea has been struck by a 3.4 scale quake that China says may have been caused by an explosion.
The natural disaster was detected in Kilju county in North Hamgyong Province, where North Korea's known Punggyeri nuclear site is located, the official said.
The first sign Pyongyang has conducted a nuclear test is usually seismic activity. But the official from the South Korean agency said the analysis of seismic waves and the lack of sound waves clearly showed that the quake wasn't caused by an artificial explosion.
SIPRI says that as of January 2017 the United States, Russia, Britain, France, China, India, Pakistan, Israel and North Korea together had about 14,935 nuclear weapons, down from 15,395 a year earlier. "We can not conclusively confirm at this time the nature (natural or human-made) of the event".
South Korea's weather agency, however, said it was examining the quake and took the view that it was a naturally occurring phenomenon.
"A key method is to look at the seismic waves or seismic acoustic waves and the latter can be detected in the case of a manmade quake". The last test on Sept.3 registered as a 6.3 magnitude quake.More news: Your time will come, Jose Mourinho assures Ander Herrera and Michael Carrick
But on the fringes of the United Nations meeting this week, North Korean Foreign Minister Ri Yong-ho upped the tensions further, telling reporters Pyongyang might now consider detonating a hydrogen bomb outside its territory.
A secondary tremor detected after that test could have been caused by the collapse of a tunnel at the mountainous site, experts said at the time.
The U.S. Geological Survey said it could not conclusively confirm whether the quake, which it measured at magnitude 3.5, was man-made or natural.
Kim on Friday threatened the "highest level of hard-line countermeasure in history" in a tirade against Trump's warning that Washington would "totally destroy" the North if the USA or its allies were threatened.
On Thursday Trump announced new USA sanctions that he said allow targeting of companies and institutions that finance and facilitate trade with North Korea. It will also ban imports of textiles from North Korea.
North Korea said its recent nuclear test was a detonation of a thermonuclear weapon built for its developmental intercontinental ballistic missiles.