SEOUL (Yonhap) -- North Korea's military has erected two surveillance towers along the Joint Security Area (JSA) near the border village of Panmunjom to better monitor South Korean military in the Demilitarized Zone (DMZ), a military official said Sunday.

The 60-meter-high steel towers equipped with security cameras were set up in December last year inside the North's portion of the JSA, the official said on the condition of anonymity.

The towers were erected following the defection of two North Korean soldiers who crossed the border into South Korea after killing their senior officer last October, the official said.

The official said the North's move appears to strengthen its monitoring of the border area.

"The objective is believed to be aimed at strengthening surveillance of its own areas and better monitoring movements of our personnel going in and out of the Panmunjom," the official said.

North Korea had installed 20-meter-high steel towers for such monitoring.

South Korea's military is considering erecting more surveillance towers in response to the North's new towers, according to the official.

The JSA is considered one of the last Cold War frontiers where the 1953 Korean Armistice Agreement was signed.