The U.S. Geological Survey said it recorded a 6.3-magnitude quake on Sunday, described as a "possible explosion", near North Korea's known nuclear test site in the northeast.
But Japanese Prime Minister Shinzo Abe told reporters that he had spoken with Trump by phone and said close cooperation between their countries and South Korea was needed in face of the "escalating" situation with North Korea.
North Korea carried out two nuclear tests last year, the last almost a year ago, on the 9 September anniversary of the nation's founding.
The same news outlet published images earlier Sunday showing leader Kim Jong-un inspecting a new H-bomb warhead.
The blast, which came almost a year after the North's fifth nuclear test, appeared to be the most powerful yet, according to South Korea's weather agency. South Korea's military said it has strengthened its monitoring and readiness while mulling a variety of possible responses that could be executed in collaboration with the U.S.
North Korea's Hwasong-14 is a powerful ICBM that can range most of the continental USA, according to leading experts.
Bachelor in Paradise's Corinne Olympios Apologizes To DeMario Jackson
But I was also on a medication that severely blacks you out and impairs your judgment and messes with your balance. What's more , it's hard to imagine a motivation for doing so beyond stretching out the drama for ratings.
Juche is North Korea's homegrown ruling ideology that is a combination of Marxism and extreme nationalism preached by state founder Kim Il Sung, the current leader's grandfather.
South Korean President Moon Jae-in offered talks to Kim in July, but North Korea hasn't responded.
However, U.S. officials remain skeptical of the claims, with many left questioning whether Pyongyang has actually managed to successfully miniaturise its weapons, or whether it even has a working H-bomb.
The weapon is also said to have been built with North Korean-made components, a fact that means the country can build as many nuclear weapons as it wants.
South Korea's National Intelligence Service warned Monday that its neighbor might be preparing its sixth nuclear weapon test from a nuclear test site in Punggye-ri.
- Agrees to Private Interview With Senate Judiciary Committee
- Rohingya die after boat carrying them capsizes in Bangladesh
- Florida suspends Jordan Scarlett and Rick Wells
- 'Blade Runner 2049' prequel short introduces us to Niander Wallace
- Blame Harvey or Canada, but we'll likely have rain this weekend
- US, UK and 22 other envoys laud Supreme Court decision
- Next stop Earth for NASA's space champ
- Georgia vs Republic of Ireland Match updates
- United States To Withdraw Free Trade Deal With South Korea
- Final Score 4-0, City players quiet in England win