NORTH KOREA—The U.S. Geological Survey noticed unusual results, which led to a shocking announcement by leaders in North Korea.
The agency reported a seismic event Monday near a site known for nuclear tests by North Korea.
Officials in North Korea announced it has carried out its third successful nuclear test.
North Korean television says it was more powerful than earlier blasts but the device was smaller in size and lighter.
If the underground test is confirmed, it would be the first nuclear test under Kim Jong Un.