South Korean soldiers fired warning shots after North Korean troops crossed the border and then retreated, in the third such incident this month on the heavily armed peninsula.Several North Koreans working within the Demilitarized Zone buffer that separates the two countries crossed into South Korea’s territory on Thursday and retreated after being warned verbally,

Some North Korean soldiers who were engaged in unspecified work on the northern side of the border briefly crossed the military demarcation line on Sunday, the South Korean military said.

This is the second border violation by North Korean troops this month, amid surging tensions between Seoul and Pyongyang.