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

The North Korean leader's powerful sister said on Thursday that the country has never taken down propaganda loudspeakers and will not do so, calling South Korea's belief that Pyongyang was responding to its peace overtures a "pipedream.