North Korean leader Kim Jong Un has entrenched his daughter as heir apparent ahead of a landmark party conference, a South Korean lawmaker said on Thursday after a briefing from Seoul's main intelligence agency.

The Kim family has ruled North Korea with an iron grip for decades, and a cult of personality surrounding their "Paektu bloodline" dominates daily life in the isolated country.

Kim's teenage daughter Ju Ae has long been seen as the next in line, a perception stoked by a string of recent high-profile outings. 

South Korea's National Intelligence Service said Ju Ae has now been clearly "designated as a successor", lawmaker Lee Seong-kweun said after a parliamentary briefing with the spy agency. 

The assessment was made "taking into account a range of circumstances -- including her increasingly prominent public presence at official events", he told reporters. 

There were also signs that Ju Ae had started to weigh in on discussions of government policy, he said. 

South Korea's spy agency said last year Ju Ae appeared to be the next in line after she accompanied Kim on a high-profile visit to Beijing.

Photos published ahead of a rare political congress in North Korea this month cemented that view.

State media showed Ju Ae in January paying respects alongside her father at the Kumsusan Palace of the Sun, where the bodies of state founder Kim Il Sung and second-generation ruler Kim Jong Il lie in state. 

Pyongyang is due to hold a landmark party congress at the end of February -- its biggest political event -- where it is expected to lay out its foreign policy, war planning and nuclear ambitions for the next five years. 

The National Intelligence Service said it would closely monitor Ju Ae's attendance, as well as the level of protocol accorded to her.  

Analysts have suggested that she could be elected First Secretary of the Central Committee, the second most powerful position in North Korea's ruling Workers' Party. 

Ju Ae was publicly introduced to the world in 2022 when she accompanied her father to an intercontinental ballistic missile launch.

'Beloved child'

North Korean state media have since referred to her as "the beloved child" and a "great person of guidance" -- "hyangdo" in Korean -- a term typically reserved for top leaders and their successors.

Before 2022, the only confirmation of her existence had come from former NBA star Dennis Rodman, who visited the North in 2013.

South Korea's National Intelligence Service first acknowledged Ju Ae as Kim's likely successor in 2024.

The call took many by surprise, given that Seoul has long painted North Korea as a male-dominated society unlikely to embrace a female leader. 

Pyongyang has never confirmed Ju Ae's exact age, but analysts believe she is in her early teens.

Most estimates put Ju Ae's birthday somewhere between 2012 and 2013.

Ju Ae has drawn attention for her taste in luxury fashion, appearing in Gucci sunglasses and wearing Cartier watches.

At other times, she has mirrored her father's distinctive style, wearing matching leather jackets and dark glasses. 

Footage released this year showed Ju Ae accompanying her parents at New Year celebrations in Pyongyang.

While first lady Ri Sol Ju kept a low profile, state TV showed Ju Ae placing one hand on the North Korean leader's face and kissing him on the cheek -- a rare public display of affection.