Korea border
A visitor walks in front of a directional sign showing the distance to North Korea's Kaesong city and South Korea's capital Seoul near the wire fences decorated with ribbons written with messages wishing for the reunification of the two Koreas at the Imjingak Pavilion in Paju, South Korea, Sunday, June 14, 2020. Image Credit: AP

Seoul: North Korea blew up an inter-Korean liaison office on its side of the border on Tuesday, the South's Unification ministry said, after days of increasingly virulent rhetoric from Pyongyang.

"North Korea blows up Kaesong Liaison Office at 14:49," the ministry, which handles inter-Korean relations, said in a one-line alert sent to reporters.

The statement came minutes after an explosion was heard and smoke seen rising from the long-shuttered joint industrial zone in Kaesong where the liaison office was located, Yonhap news agency reported citing unspecified sources.

Its destruction came after Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, said at the weekend: "Before long, a tragic scene of the useless north-south joint liaison office completely collapsed would be seen."

Since early June, North Korea has issued a series of vitriolic condemnations of the South over activists sending anti-Pyongyang leaflets over the border - something defectors do on a regular basis.

Last week it announced it was severing all official communication links with South Korea.

The leaflets - usually attached to hot air balloons or floated in bottles - criticise North Korean leader Kim Jong Un for human rights abuses and his nuclear ambitions.

Analysts say Pyongyang may be seeking to manufacture a crisis to increase pressure on Seoul while nuclear negotiations with Washington are at a standstill.

Earlier Tuesday, North Korea's army said it was "fully ready" to take action against the South, included re-entering areas that had been demilitarised under an inter-Korean agreement.

"North Korea is frustrated that the South has failed to offer an alternative plan to revive the US-North talks, let alone create a right atmosphere for the revival," said Cheong Seong-chang, a director of the Sejong Institute's Center for North Korean Studies.

"It has concluded the South has failed as a mediator in the process.