The sister of North Korean leader Kim Jong-un has reportedly slammed South Korea's presidential office for protesting over the North's recent projectile launches, saying the firing drill was an act of self-defense.

In the first-ever official statement issued under her name on Tuesday, Kim Yo-jong, the first vice department director of the Central Committee of the North's ruling Workers' Party, claimed that it makes no sense for the South to take issue with the North's self-reliant exercises.

In the statement carried by the North's official Korean Central News Agency on Tuesday, Kim strongly criticized the South Korean top office for expressing concerns and calling on the North to halt such exercises. 

Kim referred to the top office's statement as "truly shocking" and a "senseless act" that would only "magnify the North's distrust, hatred and scorn for South Korea." She noted that the South, too, conducted military drills, sometimes jointly with the United States. 

Seoul's presidential office said earlier on Monday that the North's recent launches were "unhelpful for efforts to ease tensions on the Korean Peninsula" and called on Pyongyang to halt them. 

Kim also said that the joint military exercise between South Korea and the U.S. slated for this month was postponed because of the COVID-19 outbreak in the South. She continued that such a decision could never have been made by the owners of Cheongwadae, claiming they are indifferent to peace, reconciliation and cooperation.