N Korea preparing to conduct 4th nuclear test but may not do so: Seoul

North Korea is making final preparations to conduct its fourth nuclear test but may not do so, South Korea's defence minister said today.

Defence Minister Kim Kwan-jin told South Korean journalists that North Korea could detonate a nuclear device the instant the decision is made, though he didn't elaborate on what the final step of those preparations was, according to ministry officials.

Kim also said North Korea may hold off on a test or it may be aiming to trick outside observers into believing it will explode a device even though it doesn't intend to do so, the officials said requesting anonymity citing department rules.

North Korea has threatened in recent weeks to conduct a nuclear test to protest what it calls US and South Korean hostility and international condemnation over its rocket and missile tests earlier this year.

Many North Korea watchers had suspected a nuclear test would occur when President Barack Obama visited Seoul last month but nothing happened.

Analysts remain divided over whether North Korea would go ahead with a test anytime soon. But the test, if made, would mark another defiant response to US-led international pressures on Pyongyang to abandon its nuclear weapons program.

North Korea conducted nuclear tests in 2006, 2009 and 2013.

Western experts believe North Korea has a handful of rudimentary bombs though it's not yet believed to acquire a technology to manufacture warheads small enough to mount a missile that could threaten the US.

Recent months have seen a flare-up of animosities on the Korean Peninsula with Pyongyang conducting a barrage of rocket and missile tests and resuming fierce rhetoric against Seoul and Washington.

Before then, the North had been gradually dialling down its threats and seeking improved ties with South Korea in what foreign analysts say is an attempt to lure investment and aid.

A year ago, Pyongyang made a torrent of threats to launch nuclear strikes against Seoul and Washington in protest of UN sanctions that were toughened over its third bomb test.