SEOUL: North Korean leader Kim Jong Un appears to be taking steps to consolidate his daughter's position as successor, and there are signs she is providing input on policy matters, South Korean lawmakers said on Thursday, citing a spy agency briefing.

South Korea's National Intelligence Agency (NIS) will be closely watching whether the daughter, believed to be named Kim Ju Ae, attends an upcoming meeting of the ruling Workers' Party and how she is presented, including whether she takes on any official title, the lawmakers said.

"In the past, the NIS described Kim Ju Ae as being 'in study as successor' but today the expression used was that she 'was in the stage of being internally appointed successor'," lawmaker Lee Seong-kweun told reporters following a closed-door briefing from the NIS.

Ju Ae, who is believed to be in her early teens, has been increasingly prominently featured in North Korea's state media accompanying her father on field guidance including inspections of weapons projects amid speculation by analysts that she is being groomed as the country's fourth-generation leader.

The NIS believes the role she has taken on during public events indicates she has started to provide policy input and that she is being treated as the de facto second-highest leader, Lee and another lawmaker Park Sun-won said.

North Korea has announced the Workers' Party will convene the inauguration meeting of the ninth Congress in late February, an event that analysts believe will unveil major policy goals for coming years on the economy, external affairs and defence.

Leader Kim Jong Un is directing the development of a large submarine that is likely capable of carrying up to 10 submarine-launched ballistic missiles (SLBM) and which, considering the vessel's displacement of 8,700 tons, may be designed to be powered by a nuclear reactor, Park and Lee said.

It remains unclear, however, whether it will be nuclear powered or operationally functional as designed, the lawmakers said, citing the spy agency's analysis.