Kim Yo Jong, the younger sister of North Korean leader Kim Jong Un, calls out the South Korean government "truly weird group" during a significant conference. 

The event took place while her brother, North Korean leader Kim Jong Un vowed all-out efforts to improve his country's nuclear arsenal. He previously laid out plans to work towards salvaging the broken economy.

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Separately, South Korea's military was blamed by Kim's influential sister for claiming it had seen an apparent military parade taking place in Pyongyang. In a statement Wednesday, Kim Yo Jong, who was identified as being in charge of inter-Korean relations last year, said that such close monitoring proved Seoul's "hostile approach" to its rival.

Kim Yo Jong is one of the country's most influential political figures, denounced the "idiot" authorities in South Korea after drawing attention to an apparent military parade held over the weekend in Pyongyang, the capital.

"We are only holding a military parade in the capital city, not military exercises targeting anybody nor launch of anything. Why do they take trouble craning their neck to follow what's happening in the north," Kim said in a statement published by North Korea's state-run news agency, KCNA.

"The southerners are a truly weird group (and) hard to understand."

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Comments from Kim Yo Jong were released as the Eighth Workers' Party Congress, a significant week-long North Korean political affair, came to a close. The Congress is held for the rulers of North Korea to meet and reflect on past years' achievements and shortcomings and set a plan for the near future. Usually, they're held every five years or so, but after 1980, Kim's father and predecessor, Kim Jong Il, stopped keeping them. In 2016, Kim Jong Un revived the gatherings.

Experts had hypothesized that North Korea could mark the top of Congress with an army parade. Still, no pictures or video of such an occasion had been released by North Korean state media as of Wednesday afternoon on the Korean Peninsula.

Kim Yo Jong seemed to prove that a parade had taken place while criticizing the South for wasting its time, although these parades offer precious clues about the weapons programs of the famously hidden government. Kim also claimed that Seoul's espionage was reflective of its "hostile approach to fellow countrymen in the north."

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Kim was thought to be one of the strongest and trusted confidants of her brother. Still, experts are uncertain what to make of her standing after the Party Congress, which noticed her being removed from the highly efficient political bureau of North Korea as an alternate and demoted from "first vice department director" to "vice department director.

The fate of Kim Yo Jong in North Korea's politics remains uncertain following the big political event in North Korea last week. In recent days, she did not even appear in the newly published lineup of Kim Jong Un for the country's influential Politburo.

Oh Gyeong Seob, an analyst at the Seoul Korea Institute for National Unification, said that according to the Associated Press report, Kim Yo Jong's rumors of being the heir of her brother could be dangerous because they "raise the issue of Kim's hold on power and health within North Korea." The North Korean leader is, therefore, slowing her rise to power, according to the analyst.