South Korea's spy agency currently considers North Korean leader Kim Jong-un's daughter, Kim Ju-ae, to be his most probable successor.

National Intelligence Service(NIS) director nominee Cho Tae-yong delivered the assessment in a written response ahead of his parliamentary confirmation hearing on Thursday, citing a comprehensive analysis of the daughter's public appearances and level of courtesy.

This is the first time that Korea's spy agency has publicly judged Kim Ju-ae to be the most likely successor.

The nominee added, however, that Seoul is keeping a close observation as the regime leader is young and in relatively good health, among many other variables.

Aside from Ju-ae, born in 2013, the regime leader is understood to have another child whose gender remains unidentified.

As for the North's additional nuclear test, Cho said Pyongyang is maintaining its Punggye-ri facility to enable testing at any time, and the timing will likely be decided by the political considerations of the regime leader.