SEOUL (AFP) — South Korean troops fired warning shots after North Korean soldiers briefly crossed the border this week, Seoul’s military said Tuesday, with tensions high over Pyongyang’s trash-carrying balloons and the South’s retaliatory loudspeaker campaign.

The Sunday incursion over the line separating the two militaries took place in an overgrown area of the heavily fortified border area and was likely accidental, the Joint Chiefs of Staff (JCS) said.

“Some North Korean soldiers working within the DMZ on the central front briefly crossed the Military Demarcation Line (MDL),” the JCS said in a statement, referring to the line of control between the two Koreas.

“After our military issued warning broadcasts and warning shots, they retreated northward,” it said, adding there had been “no unusual movements observed” subsequently.

The incursion was likely accidental, JCS spokesperson Lee Sung-joon told reporters Tuesday.

“The situation at that time was that the DMZ was now overgrown with trees and the MDL mark was not clearly visible,” Lee said.

“There was no road, and the (North Korean soldiers) were moving through the bushes, and we were observing (them) even before they got close to the MDL,” Lee said.

“We believe that they did not intend to invade, considering that they immediately moved northward after the warning broadcasts and warning shots.”