South Korea's defense ministry says it has upped its defense readiness and is keeping a close eye on any unusual movement north of the border.
It also says it is working in close coordination with the U.S.
"In close collaboration under the South Korea-U.S. alliance and with the international community, our military will take necessary measures to make North Korea pay for the nuclear test."
South Korea's defense ministry said that North Korea is always capable of conducting a nuclear test at any given time, so it was hard to predict exactly when Pyongyang would conduct another nuclear test.
The ministry also said that it is unlikely that North Korea conducted a full-scale hydrogen bomb test, as an H-bomb is one-hundred to one-thousand times stronger than an atomic bomb, and added that it's hard to believe Pyongyang has obtained the technology.
Military officials added that only a few countries including the U.S. and Russia have tested hydrogen bombs and the size of the detonations reached up to 50 megatons while North Korea's test only reached 6 kilotons.
He did say, that although there could be some hydrogen particles,these don't belong to a full H-bomb.
The recent blast recorded a 4.8 on the seismic graph, which is zero.one point lower than the nuclear test it conducted in 2013.
Wednesday's test will be the fourth nuclear test conducted by North Korea, following those in 2006, 2009, and 2013. Kim Hyun-bin, Arirang News.