About 20 North Korean soldiers briefly crossed the inter-Korean land border earlier this week and went back to the North's side after the South's military fired warning shots, the Joint Chiefs of Staff said Tuesday.

The North Korean soldiers crossed the Military Demarcation Line within the Demilitarized Zone separating the two Koreas in the central section of the border at around 12:30 p.m. Sunday, according to the Joint Chiefs of Staff.

The South Korean military conducted warning broadcasts and fired warning shots, prompting the North Koreans to return to their side of the border, the JCS said, adding that there was no unusual activity after the warning shots.

JCS spokesperson Col. Lee Sung-jun said the military assesses the soldiers, who were working on an unspecified task inside the DMZ, did not intend to cross the MDL, considering that they returned immediately after the warning shots.

Lee added that the DMZ is currently thick with grass and bushes, making the MDL sign difficult to see.

The incursion took place amid heightened cross-border tensions due to North Korea's recent launches of trash-carrying balloons.

It came just hours before South Korea resumed its border loudspeaker broadcasts toward the North for the first time in six years in response to the trash-balloon campaign. (Yonhap)