North Korea again fired artillery shells near its tense sea boundary with the South on Sunday, as the influential sister of North Korean leader Kim Jong Un mocked the South's ability to detect its weapons launches.South Korea's Joint Chiefs of Staff dismissed Kim Yo Jong's statement as "a comedy-like, vulgar propaganda" meant to undermine the South Korean people's trust in the military and stoke divisions.The Joint Chiefs of Staff said North Korea fired more than more than 90 rounds near the rivals' disputed western sea boundary on Sunday afternoon. It said South Korea strongly urged North Korea to stop provocative acts immediately.North Korea's military later confirmed it used coastal artillery systems to carry out live-firing exercises. It said the drills were part of its military training schedules and the direction of its shells fired didn't expose any threat to South Korea.On Friday, North Korea launched about 200 shells. South Korea also claimed that the North fired more than 60 rounds on Saturday, but its rival has denied that.Kim Yo Jong said that North Korea on Saturday only detonated blasting powder simulating the sound of its coastal artillery on the seashore, to test the South Korean military's detection capabilities."The result was clear as we expected. They misjudged the blasting sound as the sound of gunfire and conjectured it as a provocation. And they even made a false and impudent statement that the shells dropped north" of the sea boundary, Kim Yo Jong said in a statement carried by state media."I cannot but say that (South Korean) people are very pitiful as they entrust security to such blind persons and offer huge taxes to them," she said. "It is better 10 times to entrust security to a dog with a developed sense of hearing and smell."Animosities between the two Koreas are running high because North Korea has conducted a barrage of missile tests since 2022 while South Korea has expanded its military training with the United States in a tit-for-tat cycle.North Korea's artillery firings Friday prompted South Korea to have its troops on border islands fire artillery rounds near the sea boundary in response. The shells launched by the two Koreas fell at a maritime buffer zone they had established under a 2018 military agreement on lowering front-line military tensions.The agreement requires the Koreas to halt live-fire exercises, aerial surveillance and other hostile acts along their border, but the deal is now in danger of collapsing because the two Koreas have taken measures to breach it.Experts say North Korea is likely to ramp up weapons tests and escalate its trademark fiery rhetoric against its rivals ahead of South Korea's parliamentary elections in April and the U.S. presidential elections in November. They say Kim Jong Un likely thinks a bolstered weapons arsenal would allow him to wrest greater U.S. concessions if former President Donald Trump returns to the White House.In her statement Sunday, Kim Yo Jong called South Korea's military "gangsters" and "clowns in military uniforms." She also suggested South Korea's possible future miscalculation of North Korean moves could cause an accidental clash between the rivals, jeopardizing the safety of Seoul, a city of 10 million people which is only an hour's drive from the land border.On Tuesday, Kim Yo Jong issued a statement calling South Korean conservative President Yoon Suk Yeol "foolishly brave" but his liberal predecessor Moon Jae-in "very smart." South Korean analysts say she was attempting to help muster those opposing Yoon's tougher policy on North Korea ahead of the April elections.