North Korean leader Kim Jong Un pledged to strengthen his nation's military capacities and bolster its nuclear arsenal in his closing address at the ruling Workers' Party congress, the official Korean Central News Agency reported Wednesday.

Kim's remarks were delivered at the congress, the first held in nearly five years, before it closed on Tuesday.

The news agency also said North Korea will convene a session of its top legislature, the Supreme People's Assembly, on Sunday to adopt legislation related to the nation's new five-year national economic development strategy.

Meanwhile, Kim's younger sister and close aide, Kim Yo Jong, criticized South Korea for announcing the North may have held a military parade on Sunday night on the occasion of the congress.

"The southerners are a truly weird group hard to understand," Kim Yo Jong said in a statement carried by KCNA in English, adding, "They are the idiot and top the world's list in misbehavior as they are only keen on things provoking world laughter."

"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," she said.

At the current congress, which started Jan. 5, Kim Yo Jong, was excluded from the list of alternate members of the Political Bureau of the Central Committee of the ruling party, a surprise move for North Korea's hereditary regime.

She has been seen as the front-runner to succeed her brother, given that North Korea's sacred "Mt. Paektu bloodline" is believed to allow only direct descendants of the country's founder, Kim Il Sung, to lead the nation.