China is imposing new limits on trade with North Korea after the isolated country's latest nuclear test.
South Korean media report North Korea's top diplomat says his country may test a hydrogen bomb in the Pacific Ocean to fulfill leader Kim Jong Un's vow to take the "highest-level" action against the United States.
Chinese seismologists said it was a "suspected explosion" but South Korea says that it could be a natural quake not caused by a nuclear test.
The size of Saturday's tremor is smaller than the earthquakes registered as a result of all of North Korea's six nuclear tests.
The site, run by the U.S. -Korea Institute at Johns Hopkins University's School of Advanced International Studies, added the bomb's 250-kiloton yield was close to what it previously determined was the maximum that could be contained by the test site.
The administration said in a statement on its website that the quake, which occurred around 0830 GMT, was recorded a depth of zero kilometres.
The United Nations Security Council, including permanent member Beijing, approved tough sanctions against Pyongyang last week in response to its sixth and most powerful nuclear test.
Exports of refined petroleum to the North will be limited to 2 million barrels per year and sales of liquefied natural gas banned completely effective 1 January, China's commerce ministry said.
While the cause remains unknown, alternative explanations suggested by North Korea analysts include tunnel collapses at the testing site.
- President Donald Trump ordered new sanctions on Thursday that open the door wider to blacklisting people and entities doing business with North Korea, further tightening the screws on Pyongyang's nuclear and missile programs.
"The new sanctions set a cap on crude and refined oil exports to North Korea at 8.5 million barrels per year, which represents a 30 percent reduction, according to USA officials". Its leaders say nuclear capabilities are its only deterrent against an outside world seeking to destroy it.
European Union ambassadors have reached an initial agreement to impose more economic sanctions on North Korea, going beyond the latest round of United Nations measures, officials and diplomats said on Thursday.