President Park Geun-hye said Monday that South Korea has detected signs of North Korea preparing for a fifth nuclear test.

We are in a situation, in which we don't know whether North Korea could stage any provocation to avoid isolation and consolidate its internal unity," Park said in a regular meeting with her top aides at Cheong Wa Dae, South Korea's presidential office.

She also said signs of "preparations for a fifth nuclear test have been detected."

Park's comments came more than a month after the U.N. Security Council imposed the toughest-ever sanctions resolution on North Korea for its nuclear test and a long-range rocket launch earlier this year.

Park called on the military to maintain readiness to sternly retaliate against North Korea in case Pyongyang stages a provocation.

Park has warned that North Korea could face even tougher sanctions and isolation should it choose to undertake yet another provocation. (Yonhap)