Seoul | South Korea says North Korea has fired artillery shells near the rivals' tense sea boundary for a third straight day.
South Korea's military says the North fired more than 90 rounds on Sunday afternoon.
It says South Korea strongly urges North Korea to halt provocative acts.
The influential sister of North Korean leader Kim Jong Un mocked South Korea's ability to detect weapons launches by the North on Sunday, as she denied Seoul's claim that North Korea fired artillery shells into the sea the previous day.
South Korea's military quickly dismissed her statement as “a low-level psychological warfare” and warned that it will make a stern response to any provocations by North Korea.
South Korea's military earlier said North Korea fired shells near the rivals' disputed western sea boundary for a second consecutive day on Saturday. The military said North Korea fired more than 60 rounds on Saturday, a day after launching more than 200 shells.
North Korea acknowledged it performed artillery firings on Friday but said it didn't fire a single round on Saturday.
Kim's sister, Kim Yo Jong, said Sunday that North Korea only detonated blasting powder simulating the sound of its coastal artillery at 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.”
South Korea's Joint Chiefs of Staff responded in a statement that it closely monitors North Korean military activities. It said North Korea must stop acts that escalate tensions, saying it will “overwhelmingly” react if North Korea launches provocations.
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 carry out its own firing exercises. The shells launched by the two Koreas fell at a maritime buffer zone they had established under a 2018 military agreement meant to ease front-line military tensions.
The agreement was meant to halt live-fire exercises, aerial surveillance and other hostile acts along their tense border, but the deal is now in danger of collapsing because the two Koreas have taken measures in breach of the accord.
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 US presidential elections in November.
They say Kim Jong Un likely thinks a bolstered weapons arsenal would allow him to wrest greater US concessions when diplomacy resumes.
In her statement on 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, jeopardising 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.
