South Korea's defense minister warned that North Korea has completed preparations for its fourth nuclear test and said a detonation could occur the moment Pyongyang makes the decision.
But, Kim Kwan-jin said on Thursday, it could be some time before North Korea goes ahead with the test, noting that the preparations could be meant to deceive the outside world.
"Some experts say North Korea's physical preparations related to the nuclear test are deceptive and are meant as tricks. But from the government's point of view, we cannot help but be nervous and prepare for the fact that North Korea has completed the preparations," Kim said.
Recent satellite imagery has shown increased activity at North Korea's main nuclear test site. However, such intelligence is often unreliable, and the behavior of North Korea's leaders is famously unpredictable.
North Korea has conducted nuclear tests in 2006, 2009 and 2013 in violation of United Nations Security Council resolutions. It has threatened in recent months to conduct an unspecified new form of nuclear test.
Pyongyang is believed to be trying to perfect the technology necessary to place a miniaturized nuclear warhead on a long-range ballistic missile. Most analysts say it is many years from achieving this ability.
North Korea is thought to have used plutonium to conduct its first two underground nuclear tests, though it is unclear whether plutonium or uranium was used in the third test.
Uranium is easier and cheaper to acquire than plutonium.