The sister of North Korean leader Kim Jong Un has stressed that Pyongyang will retaliate if South Korean drones are found again in its territorial airspace.

Kim Yo Jong issued a statement through the state-run Korean Central News Agency on Saturday reports NHK.

The North's foreign ministry claimed a day earlier that South Korean drones flew over Pyongyang and scattered propaganda leaflets earlier this month. South Korea's military said it could not confirm Pyongyang's claim.

Kim accused the South of making a "childish excuse," and alleged that even if the drones were flown by a non-governmental organization, the "infiltration" was carried out with the South Korean military's "connivance."

She warned that if a South Korean drone is detected over her country's capital once again, it will lead to a "horrible disaster."

The South Korean military had urged the North Korean side to exercise self-restraint over the matter, warning that it will respond sternly if people's safety comes under threat.