South Korea’s birth rate has dropped throughout much of the past decade, spelling trouble for the military as regional threats and global conflicts simmer.

In a speech to mark the 80th anniversary of Korea's liberation from Japanese colonial rule, Lee said he would restore the so-called September 19 Comprehensive Military Agreement, a de-escalation measure that halted some military activities at the border between North Korea and South Korea.

South Korean President Lee Jae Myung vowed on Friday to "respect" North Korea's political system and build "military trust", a day after Pyongyang said it had no interest in improving relations with Seoul.