South Korean soldiers fired warning shots after North Korean troops violated the border earlier this week, according to media reports.

Yonhap news agency reported on Tuesday that North Korean soldiers briefly crossed the heavily fortified border before retreating back to their territory on Sunday.

Seoul’s military said South Korean soldiers fired warning shots at the time.

“Some North Korean soldiers working within the DMZ on the central front briefly crossed the Military Demarcation Line. After our military issued warning broadcasts and warning shots, they retreated northward,” Seoul’s Joint Chiefs of Staff (JCS) said.

The North Korean soldiers did not appear to have intentionally crossed the border because the site is a wooded area and MDL signs there were not clearly visible, Joint Chiefs of Staff spokesperson Lee Sung Joon told reporters.

The incident comes amid rising tensions over North Korea’s recent launches of balloons filled with rubbish.

North Korea began sending balloons carrying waste and animal faeces south across the border last month in response to propaganda sent north by South Korean activists.

South Korea resumed loudspeaker broadcasts on Sunday, blaring K-pop music and world news toward the northern side.