North Korea's artillery units near the border with South Korea have been ordered to be ready to fire amid frictions over drones that Pyongyang says are being flown over the frontier, state media cited the government as saying on Sunday.

Some defectors and activists in South Korea fly aid parcels into the North and drop leaflets criticizing leader Kim Jong Un.

North Korea has blamed the South Korean military for the practice. It has also been floating balloons with trash into the South in reprisal.

North Korean state news agency KCNA quoted the defense ministry's spokesperson as saying Pyongyang sees a high likelihood of more drones flying over the capital, with its military told to prepare for all scenarios including conflict.

On Friday, North Korea accused South Korea of sending drones into Pyongyang at night this week and last, and said the intrusion demanded retaliatory action.

Kim Yo Jong, powerful sister of North Korean leader Kim Jong Un, warned Seoul on Saturday of a "horrible disaster."

She said the blame lies with the South Korean military if it failed to identify drones sent by a non-governmental organization crossing the border.

South Korea's Joint Chiefs of Staff said it could not confirm the North's accusations.