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.

South Korea will end some military activities along its border with North Korea, President Lee Jae Myung said on Friday, in his government's latest effort to improve ties between the neighbours still technically at war.

South Korean President Lee Jae Myung pledged to "respect" North Korea's political system and said Seoul would not seek unilateral reunification in a speech to mark Liberation Day.