South Korea's military said Tuesday it fired warning shots at a group of North Korean soldiers who briefly crossed the military demarcation line (MDL) inside the Demilitarized Zone (DMZ) dividing the two Koreas.

About 10 armed North Korean soldiers returned to the North after the South Korean military aired warning broadcasts and fired warning shots in an eastern front-line area at around 5 p.m., according to the Joint Chiefs of Staff (JCS).

The JCS said South Korea's military is "closely monitoring the movement of the North Korean military and taking necessary measures in accordance with the operational procedures."

The JCS said it suspects the North Korean soldiers' border crossing occurred accidentally while they were conducting a regular patrol.

"It appears that they were on a reconnaissance mission ahead of some preparatory work, and they may have crossed the military demarcation line by mistake due to the terrain," a military official at the JCS said.

The crossing, however, came days after South Korea's Constitutional Court ruled to remove former President Yoon Suk Yeol from office over his failed martial law bid.

The area the North Korean soldiers crossed into was near the county of Goseong in the eastern Gangwon Province, which is not an area typically known as a site where the North's soldiers are sent for road work or to clear land.

Earlier this week, South Korea's military said about 1,500 North Korean soldiers were in the final stages of training near the border while working to install barbed wire.

The DMZ is one of the most heavily guarded areas in the world, with barbed wire fences and a substantial military presence along both sides.

The MDL horizontally bisects the DMZ, which has served as a buffer zone between the two Koreas since the 1950-53 Korean War ended in an armistice, not a peace treaty.

The latest border crossing came as tensions between the two Koreas remain high after North Korean leader Kim Jong-un labeled the inter-Korean relationship as "two states hostile to each other" and has ramped up its military buildup by closely aligning with Russia.

The South's military last fired warning shots in October, when the North blew up the Gyeongui and Donghae roads, once seen as symbols of inter-Korean cooperation.