The test provoked global condemnation and led the UN Security Council to impose fresh sanctions on North Korea.
It said epicentre of the quake was nearly same with a similar little depth natural disaster on September 3, which was actually a nuclear test. On Thursday, the USA unveiled its own set of economic sanctions targeting North Korea.
However, the agency has said it has not detected any man-made sound waves and the initial view was that it was a natural tremor.
"This mission is a demonstration of USA resolve and a clear message that the President has many military options".
The agency said it is analyzing the nature of the quake.
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.
A 3.5 natural disaster has been detected in North Korea and many believe that it is another missile test.
The September 3rd test was North Korea's most powerful detonation, triggering a much stronger 6.3-magnitude quake that was felt across the border in China.
All of North Korea's previous six nuclear tests registered as earthquakes of magnitude 4.3 or above.
People walk by a screen showing the news reporting about an natural disaster near North Korea's nuclear facility, in Seoul, South Korea on January 6, 2016.
Tensions have been high between North Korea and the United States since July, when the North test-fired two ICBMs purportedly capable of targeting the mainland US.
Hydrogen bombs, or H-bombs, are thermonuclear weapons far more powerful than ordinary fission-based atomic bombs, and use a nuclear blast to generate the intense temperatures required for fusion to take place.
On Friday, Donald Trump publicly branded the North Korean leader Kim Jong Un a "rocket man" and said American "really had no choice" but to confront the authoritarian regime.
President Donald Trump is again assailing North Korea Kim Jong Un, saying that he "will be tested like never before".
His comments came after Trump ordered new sanctions on individuals, companies and banks doing business with North Korea as he sought to further isolate the regime and increase economic pressure for it to curb its weapons programs.
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.
The latest alert comes amid heightened tensions in the Korean peninsula.
There was no immediate reaction from China's Foreign Ministry, but the news was widely reported by Chinese state media outlets and on social media. 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.