Barbed and concertina wire top fencing close to the Imjin River near the Demilitarized Zone between North and South Korea in this photo from May 2017. (Aaron Kidd/Stars and Stripes)

South Korean troops fired warning shots at two North Korean soldiers who briefly crossed the fortified inter-Korean border not long after another soldier defected to the South in that area, South Korean authorities said Monday.

The two soldiers came within 220 yards of a South Korean guard post on Oct. 19, a Ministry of National Defense spokesman told reporters during a routine briefing.

“We issued warning broadcasts and fired warning shots, and they immediately retreated,” he said. Some South Korean government officials are required to speak to media on condition of anonymity.

Earlier that day, a defecting North Korean soldier crossed inside the Demilitarized Zone near the border’s central area, the spokesman said.

The defector crossed at an area without barriers, South Korean Col. Lee Sung-jun, a spokesman for the Joint Chiefs of Staff, said during at an Oct. 20 briefing.

When South Korean troops first encountered the soldier, they asked his intention and the soldier followed the team, Lee said.

South Korea’s Yonhap news agency reported Friday that the two soldiers who crossed later may have been following the defector, but the ministry spokesman said their intentions were not clear.

“The individuals who appeared later in the same area were after hours, so we cannot confirm whether the two incidents are related,” the ministry spokesman said.

He said the ministry is reviewing the incident to determine how the two soldiers came so close to the South Korean guard post.

North Korean soldiers are installing barbed wire fences near the border, but the ministry has seen no unusual activity since the Oct. 19 incident, he said.