In her first known official statement, the younger sister of North Korean leader Kim Jong-un has levelled diatribes and insults against rival South Korea for protesting her country's latest live-fire exercises.

Key points: Kim Yo-jong described South Korea's presidential Blue House as "a mere child" and "a burnt child dreading fire"

Kim Yo-jong described South Korea's presidential Blue House as "a mere child" and "a burnt child dreading fire" Ms Kim's statement was issued in her capacity as a first vice-department director of the Workers Party's Central Committee

Ms Kim's statement was issued in her capacity as a first vice-department director of the Workers Party's Central Committee Analyst Cheong Seong-chang said Ms Kim's statement "suggests that her status and influence have been expanded"

Kim Yo-jong is in charge of propaganda affairs for North Korea and has frequently appeared at her brother's major public events including summits with US President Donald Trump and other regional leaders.

But her statement carried by state media was the first of its kind and indicated a further elevation of her political status.

In the statement, she criticised South Korea's presidential Blue House for expressing strong concerns over the North's firing drills and urging it to stop acts that do not help reduce military animosities.

"As far as I know, the South side is also fond of joint military exercises and it is preoccupied with all the disgusting acts like purchasing ultra-modern military hardware," Kim Yo-jong said.

"They meant they need to get militarily prepared but we should be discouraged from military exercises. Such a gangster-like assertion can never be expected from those with normal way of thinking."

Describing the Blue House as "a mere child" and "a burnt child dreading fire", she questioned how its words and actions could be "so perfectly foolish in detail".

Ms Kim did not name liberal South Korean President Moon Jae-in, whom she has met several times.

She only said: "The South side's response is so regretful and disappointing but it is somewhat fortunate that it was not a direct statement of the President."

South Korea's Unification Ministry, which handles inter-Korean affairs, said it had no specific comment on Ms Kim's statement.

North Korea fired two suspected short-range ballistic missile launches earlier this week. ( AP: Lee Jin-man )

But spokesman Yoh Sang-key said the two Koreas should maintain mutual respect while working toward establishing peace on the Korean Peninsula.

North Korean state media said Mr Kim supervised a live-fire rocket artillery exercise in an apparent reference to the two suspected short-range ballistic missile launches detected by South Korea's military.

On Saturday, North Korea said Mr Kim also guided an artillery drill aimed at testing the combat readiness of military units.

The back-to-back firing exercises were an apparent show of force by Mr Kim, who had earlier vowed to bolster his nuclear deterrent and warned of "shocking action" over now-stalled nuclear negotiations with Mr Trump.

The latest firing drills were his first weapons tests since late November.

'Kim Yo-jong's influence expanded'

Ms Kim's statement was issued in her capacity as a first vice-department director of the Workers Party's Central Committee.

Kim Yo-jong levelled insults against rival South Korea in her first known official statement. ( (Pyongyang Press Corps Pool via AP, File Photo )

She also serves as an alternate member of the North's powerful Politburo and a member of the rubber-stamp parliament.

South Korean officials and experts say she's virtually the North's top propaganda official.

Analyst Cheong Seong-chang, from South Korea's private Sejong Institute, said Ms Kim's statement "suggests that her status and influence have been expanded to such an extent as to express her opinions externally and beyond playing a role of assisting Chairman Kim Jong-un on his public activities".

Believed to be in her early 30s, Ms Kim took a prominent role at a series of summits with Mr Trump, Mr Moon and Chinese President Xi Jinping since North Korea entered talks on the fate of its advancing nuclear arsenal in 2018.

During one of the three summits with Mr Moon in 2018, Ms Kim handed her brother a pen when he signed the guestbook, and took his gloves after he shovelled dirt on a ceremonial tree and a bouquet of flowers that he had been handed at the border.

Her proximity to her brother during the summit sparked outside speculation that she may be the number two in the North after her brother executed and purged potential rivals who could pose a threat to his family's rule.

Earlier in 2018, she came to South Korea to attend the opening ceremony of the Pyeongchang Winter Olympics, becoming the first member of the North's ruling family to visit the South since the end of the 1950-53 Korean War.

At the time, she met Mr Moon and conveyed her brother's invitation to meet in Pyongyang.

AP/ABC