It said the operation showed the seriousness with which it took North Korea's "reckless behavior".
The natural disaster 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 global alarm.
The first sign Pyongyang has conducted a nuclear test is usually seismic activity. The quake was about three miles deep, and it is was located in the same vicinity as a September 3 nuclear test that registered as a magnitude 5.3 quake.
The tremor occurred at 4.29 p.m. The depth of the natural disaster was 5 kilometers (3.1 miles).
The U.S. Geological Survey said it could not conclusively confirm whether the quake, which it measured at magnitude 3.5, was man-made or natural. "We can not conclusively confirm at this time the nature (natural or human-made) of the event". The last test on Sept 3 registered as a 6.3 magnitude quake. The larger one had a 3.4 magnitude, the group's initial assessment found, which is much smaller than anything declared as a nuclear test in previous years. The locations are around 50 kilometers away (more than 30 miles) from the site of previous nuclear tests, the group said.
The US Geological Survey said on Saturday it could not conclusively confirm whether a magnitude 3.5 quake detected in North Korea was manmade or natural. They believe the activity was the result of a natural quake.
Park said analysts could not rule out the possibility that a natural quake occurred because of a nuclear test.
"Recent steps in the nuclear disarmament field are encouraging", said Shannon Kile, head of SIPRI's Nuclear Weapons Project.
North Korea's Foreign Minister Ri Yong Ho, now in NY for a United Nations meeting, warned on Thursday that Kim could consider a hydrogen bomb test of an unprecedented scale over the Pacific.
Earlier Friday, Kim issued a rare statement calling Trump "deranged" and said he will "pay dearly" for his threats to destroy North Korea.
"I am now thinking hard about what response he could have expected when he allowed such eccentric words to trip off his tongue", Kim said. Trump tweeted Friday that Kim was "obviously a madman" who would be "tested like never before".
The United States and South Korea are technically still at war with North Korea because the 1950-53 Korean conflict ended with a truce and not a peace treaty.
"Trump, the president of so-called "power, ' is mad enough to wag his tongue without any consideration that he would 'totally destroy" a sovereign state". That was a big concession by China and going to war against Kim now would have consequences far beyond the crisis on the Korean peninsula.
"The fire roughnecks who enjoy playing with fire, will die in fire", the news agency said.
North Korea has launched dozens of missiles this year, several flying over Japan, as it accelerates its program aimed at enabling it to target the United States with a nuclear-tipped missile.
An attack on North Korea now would undercut the recent decision by China to suspend financial transactions with the North and ban oil exports and textile imports.
North Korea's official news agency has ridiculed the recent United Nations sanctions as "the dirty excrement of the reactionaries of history".
"We have to assume they *could* do it, but it is exceedingly provocative", said Vipin Narang, an associate professor of political science at Massachusetts Institute of Technology.
"This mission is a demonstration of USA resolve and a clear message that the President has many military options to defeat any threat", said Pentagon spokeswoman Dana White, calling North Korea's weapons program "a grave threat".