North Korean soldiers crossed the inter-Korean border briefly on Sunday and retreated after South Korea fired warning shots.

According to the South Korean defense ministry on Tuesday, a group of North Korean troops, who were engaged in unspecified work within the Demilitarized Zone(DMZ), crossed the Military Demarcation Line at around 12:30 p.m. Sunday. 

The North Korean soldiers returned to their territory after the South Korean military broadcast verbal warnings and fired warning shots.

The ministry added that there was no unusual activity after the warning shots. 

The South Korean military said that it is taking necessary measures in accordance with standard operating procedures, while closely monitoring the movements of the North Korean troops.