North Korean soldiers build a bridge in the demiliterized zone that separates two Koreas in this photo released by Joint Chiefs of Staff on June 18. Yonhap

North Korean troops working in the Demilitarized Zone (DMZ) separating the two Koreas have briefly crossed the border into the South before returning to their side after the South fired warning shots, the Joint Chiefs of Staff (JCS) said Friday.

The North Korean soldiers crossed the Military Demarcation Line within the DMZ in the central section of the border at around 11 a.m. Thursday, the JCS said in a message to reporters.

The South Korean military conducted warning broadcasts and fired warning shots, prompting the North Korean soldiers to return to their side of the border, it said.

It marked the third border violation by the North this month after similar incidents involving a group of 20 to 30 North Korean soldiers in other areas of the central section of the border on June 9 and June 18, respectively. The JCS earlier said both cases appeared to be unintentional.

A JCS official said the latest incident also appears to be accidental, adding the soldiers soon resumed their jobs and continued working into the night after returning to the North.

Hundreds of troops were working in the nearby area when the small number of soldiers briefly crossed the border, according to the official.

"Similar situations may occur going forward as North Korean soldiers are carrying out the activities across several locations within the DMZ," the official said, adding the military is responding in a stern, principle-based manner.

The border violations came as North Korea has been deploying large numbers of troops in front-line areas since April to conduct an array of activities, such as planting mines, erecting walls assumed to be anti-tank barriers and reinforcing roads.

The JCS earlier estimated the North to have mobilized hundreds of soldiers in 10 different locations within the DMZ for such activities. It said the North appears to be pushing ahead with the work despite multiple casualties caused by mine explosions in the area. (Yonhap)

（作者：汽车音响）