The powerful sister of North Korean leader Kim Jong Un warned Saturday that Seoul would face a "horrible disaster" if unmanned drones reached Pyongyang again, a day after accusing the South of launching such aircraft at the capital.

North Korea on Friday said the South had sent drones carrying propaganda leaflets into Pyongyang's airspace on October 3, and then again on Wednesday and Thursday this week.

South Korea's Defense Minister Kim Yong-hyun initially denied the claim, but the Joint Chiefs of Staff later amended that position, saying in a statement that they "cannot confirm whether the North Korean allegations are true or not."

Kim Yo Jong, the sister of Pyongyang's leader and a key regime spokesperson, said Seoul's refusal to confirm the allegations meant that the drones were sent by "the military gangsters", referring to Seoul's forces.

"The moment that a drone of the ROK is discovered in the sky over our capital city once again will certainly lead to a horrible disaster," she added in a statement released late Saturday, using the acronym for South Korea's official name. 

The drones allegedly sent by the South had dropped anti-regime propaganda, and the leaflets were filled with "inflammatory rumors and rubbish", the North's official Korean Central News Agency (KCNA) reported on Friday.

KCNA described the incident as a "wanton violation of the international law and a grave military attack".

Despite official efforts to prevent them from doing so, South Korean activists have long flown balloons with anti-Kim propaganda leaflets and other materials, including USB sticks containing K-pop and South Korean television dramas, over the border, a tactic that the North has protested against.

In response, the North -- where the government is extremely sensitive about its people gaining access to South Korean pop culture products -- has launched more than 6,000 trash-carrying balloons southward since May.

Relations between the two Koreas are at their lowest point in years, after a military agreement meant to reduce tensions was fully suspended over the balloon incidents in June. 

North Korean leader Kim recently said that his country would use nuclear weapons "without hesitation" if attacked by the South.

In 2022, five North Korean drones crossed into the South, the first such incident in five years, prompting the South Korean military to fire warning shots and deploy fighter jets. 

The jets failed to shoot down any of the North Korean drones.