Kim Yo-jong, sister of North Korean leader Kim Jong-un, denounced the South Korean government for its “grave concerns” over the North’s recent rocket launches, saying they were part of routine self-defense exercises. It was the first time she had publicly addressed the South.

She called Cheong Wa Dae “mentally challenged” and likened it to a “frightened dog” in a statement carried by the North’s Korean Central News Agency on Tuesday. Cheong Wa Dae had expressed concerns over what Pyongyang said were its rocket launches.

Cheong Wa Dae remained silent on Kim Yo-jong’s scathing criticism, while the Unification Ministry, which handles inter-Korean affairs, highlighted the importance of mutual respect in inter-Korean relations.

North Korea experts said Kim Yo-jong was trying to rally North Koreans against the South.

“The message aims to solidify political capital for Kim Yo-jong and Kim Jong-un himself, the descendants of the fabled Paektu bloodline,” said Shin Jong-woo, a senior researcher at the Korea Defense and Security Forum.

Paektusan, a mountain on the North-China border, is a centerpiece of Pyongyang’s propaganda campaign to sanctify bloodline of the ruling Kim family. Previous ruler Kim Jong-il was born there, according to the regime’s mythology.

“Kim Yo-jong will now more frequently project herself onto the inter-Korean agenda, now that she has made a memorable debut,” Shin said.

Other experts agree that her message reflects the North’s disappointment with the South for failing to help it earn sanctions relief from the US. Pyongyang has repeatedly called on both Washington and Seoul to offer concessions for the stalled nuclear talks and inter-Korean exchanges to resume.

The previous year, Kim Yo-jong was elected first vice department director of the ruling Workers’ Party’s Central Committee at a ruling party meeting. Seoul officials suspect she is the de facto head of the party’s key organ that monitors ranking officials in the party, the military and the government.

By Choi Si-young (siyoungchoi@heraldcorp.com)