South Korea's top military officer has called for troops to stick to "basics and principles" in a New Year's message, his aide said Monday, a directive eclipsed by a botched effort to stop an unidentified person from crossing the inter-Korean border over the weekend.

For delivery on the first week of the new year, Joint Chiefs of Staff (JCS) Chairman Gen. Won In-choul had the message ready on Friday, the day before the person crossed the heavily fortified border in what is decried as yet another security lapse.

An investigation is under way to ascertain the identity of the person and why the military failed to prevent the person from moving through the barbed-wire fence into the border region despite around-the-clock surveillance operations.

"(The military) will firmly maintain an across-the-board military readiness posture while adhering faithfully to basics and principles," Won said in the message carried by the country's military newspaper, the Korea Defense Daily.

He then stressed the need for the "completeness" of security operations to deter possible enemy provocations and respond sternly if provoked.

After the border crossing, the JCS said that it became aware of the person's entry into the Demilitarized Zone (DMZ) separating the two Koreas nearly three hours after the border breach, although a surveillance camera detected the person with sensors on the barbed wire functioning properly.

The latest incident came in spite of the South Korean military's pledge to overhaul its border defense system with stronger surveillance equipment to forestall any security lapses in the wake of earlier border breaches.

In February last year, a North Korean man swam ashore into the South undetected, leading Defense Minister Suh Wook to offer a public apology. In November 2020, another North Korean civilian crossed the inter-Korean border undeterred. (Yonhap)