The North's last test, on September 3, was the country's most powerful detonation, triggering a much stronger 6.3-magnitude quake that was felt across the border in China.
The epicenter is roughly the same as that of a previous shallow natural disaster on September 3, which turned out to be caused by a North Korean nuclear test, the official Xinhua news agency said.
Earlier Saturday, U.S. Air Force B-1B Lancer bombers and F-15C Eagle fighter escorts flew in worldwide airspace over the waters east of North Korea in response to Pyongyang's "reckless behavior", Pentagon spokesperson Dana White said in a statement. We can not conclusively confirm at this time the nature (natural or human-made) of the event.
A Nuclear Test Monitoring Agency has reported two seismic events in North Korea.
The North, which says it needs nuclear weapons to protect itself against the threat of invasion by a hostile USA, responded on Friday with a rare personal rebuke from Kim, who called Trump "mentally deranged" and a "dotard" and threatened the "highest level of hard-line countermeasure in history".
President Trump has accused China of not putting enough pressure on Kim's regime to step back from its sabre-rattling.
"This is the farthest north of the Demilitarized Zone (DMZ) any USA fighter or bomber aircraft have flown off North Korea's coast in the 21st century", White said.
North Korea's state-run Korean Central News Agency published articles Saturday with comments slamming Trump.
"It could be a natural quake that really was man-made as the nuclear test would have transferred a lot of stress", he said.
On Sept. 15, North Korea launched an intermediate-range missile that flew over Japan in its longest-ever flight. "S. dotard with fire".
In a speech last week at the United Nations, Trump had issued the warning of potential obliteration and mocked the North's young autocrat as a "Rocket Man" on a "suicide mission".
"The president has said all the options are on the table".
"We can never stand by idly about it", it said.
China is imposing new limits on trade with North Korea after the isolated country's latest nuclear test.
The Chinese Ministry of Commerce said in a written statement that it will restrict exports of refined petroleum products from October 1, and ban the export of condensate oil and liquefied natural gas immediately. Earlier this month the UN Security Council unanimously adopted its ninth round of sanctions on Pyongyang to counter its nuclear and ballistic missiles 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".