Incident took place on Sunday at the Demilitarized Zone (DMZ) between the two countries.

The incident took place at about 12.30pm (03:30 GMT) on Sunday when a group of North Korean soldiers crossed over the Military Demarcation Line within the DMZ, the Yonhap news agency reported, citing a statement from the Joint Chiefs of Staff (JCS).

The JCS said South Korean soldiers broadcast warnings and fired into the air, and the North Korean soldiers returned to their side of the heavily-fortified border.

The incident comes amid heightened tensions between the two Koreas after Pyongyang sent more than 1,000 balloons filled with rubbish across the border, and South Korea resumed propaganda broadcasts which it had stopped in 2018.

Kim Yo Jong, the powerful sister of leader Kim Jong Un, said the broadcasts risked provoking a “crisis of confrontation”.

“This is a prelude to a very dangerous situation,” she said in a statement carried by state media.

North Korea is extremely sensitive to Seoul’s loudspeaker broadcasts because it fears such messaging could demoralise front-line troops and residents and eventually weaken Kim Jong Un’s grip on power, analysts say.

In 2015, the last time South Korea restarted the broadcasts after a long lull, North Korea fired artillery rounds across the border, prompting South Korea to return fire. No casualties were reported.

The JCS said there was no unusual activity after Sunday’s warning shots were fired and the soldiers returned to their side of the border.