South Korea's Unification Minister, its point man for relations with the North, resigned on Friday over heightened tensions on the peninsula, days after Pyongyang blew up its liaison office with the South.

President Moon Jae-in "accepted Unification Minister Kim Yeon-chul's offer to resign", the presidential Blue House said in a statement, without giving further details.

Kim had offered to step down on Wednesday, a day after the North demolished the liaison office, saying he "takes responsibility" for the worsening of inter-Korean relations.

Since early June, North Korea has issued a series of vitriolic condemnations of the South over anti-Pyongyang leaflets, which defectors send regularly, usually attached to balloons or floated in bottles.

Analysts say the North may be seeking to manufacture a crisis to increase pressure on the South to extract concessions.

On Tuesday it reduced the building on its side of the border that symbolised inter-Korean rapprochement to rubble, and the following day threatened to bolster its military presence in and around the Demilitarized Zone.

Inter-Korean relations have been in deep freeze for months, following the collapse of a summit in Hanoi between North Korean leader Kim Jong Un and US President Donald Trump.

That meeting foundered on what the nuclear-armed North would be willing to give up in exchange for a loosening of sanctions.

A pro-engagement academic and a longtime confidant of Moon, Kim was appointed to the post in March last year, days after the Hanoi meeting.

Reports say John Bolton, the former US national security advisor, criticised Moon in his new memoir for encouraging both Kim and Trump to have unrealistic expectations of the other.

Moon, who has also long backed engagement with the North, has been called unrealistic by his critics for his dovish approach.

On Monday the left-leaning president gave a speech calling for inter-Korean dialogue and stressing the importance of peace on the peninsula.

But Kim Yo Jong, the powerful sister of the North Korean leader, called the speech "disgusting" and "shameless and impudent", adding Moon "seems to be insane though he appears to be normal outwardly".

The two Koreas remain technically at war after hostilities in the Korean War ended with an armistice in 1953 but not a peace treaty.