Shin said North Korea probably would not risk the radioactive fallout and other dangers involved in a nuclear missile test. Ri warned Pyongyang was ready to defend itself if the USA showed any sign of conducting a "decapitating operation on our headquarters or military attack against our country".
North Korea has been maintaining a torrid pace in nuclear and weapons tests as it accelerates its pursuit of nuclear weapons that could viably target the United States and its allies in Asia.
China will limit exports of refined petroleum products to North Korea starting October 1, its commerce ministry said, confirming Beijing's participation in new United Nations sanctions meant to rein in its rogue neighbour. The depth of the quake was 5 kilometers (3.1 miles).
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. "We can not conclusively confirm at this time the nature (natural or human-made) of the event".
The quake comes after days of increasingly bellicose rhetoric between US President Donald Trump and North Korean leader Kim Jong-Un's regime over Pyongyang's nuclear ambitions that has raised worldwide alarm.
China is limiting its oil exports to North Korea after the United Nations imposed new sanctions last week, which included fuel import restrictions.
On Thursday Trump announced new USA sanctions that he said allow targeting of companies and institutions that finance and facilitate trade with North Korea. Its initial view was that it was a natural quake.
An official of South Korea's Meteorological Agency said acoustic waves should be detected in the event of a man-made natural disaster.
The CTBTO, or Comprehensive Test-Ban Treaty Organization, which monitors nuclear tests, and officials of the South Korean meteorological agency also said they believed it was a natural quake. "The waves we have detected from the latest quake have a similar pattern to that of natural earthquakes".
In comments to reporters in New York, North Korea's foreign minister said his country's leader is considering whether to demonstrate his ability to detonate a nuclear warhead aboard a missile sent above the Pacific Ocean.
As Pyongyang continues to move ahead with its nuclear programme, tension builds up in the Korean Peninsula.
North Korea's nuclear tests to date have all been underground, and experts say an atmospheric test, which would be the first since one by China in 1980, would be proof of the success of its weapons program.
"The United States has great strength and patience, but if it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea", he said. Kim Jong-un also added that the U.S. president would pay dearly for his threats.
Chinese leaders were long the North's diplomatic protectors but express increasing frustration with the government of Kim Jong Un.
North Korean textile exports in 2016 totalled 750 million dollars (£555 million), according to South Korea's Korea Trade-Investment Promotion Agency.
The president assured those in attendance, without details, that he would defend the USA against any offensives launched by North Korea: "I can tell you one thing, you are protected, OK?"
North Korea has abundant coal but depends nearly entirely on imports for oil and gas.