South Korean officials said North Korea has blown up an inter-Korean liaison office building just north of the border between the two countries.
The act has sharply raised tensions on the Korean Peninsula amid deadlocked nuclear diplomacy between Pyongyang and the United States.
Seoul’s unification ministry said the building in the North Korean border town of Kaesong was destroyed at 2.49pm local time (6.49am BST).
Photos from Yonhap News Agency showed smoke rising from what appears to be a complex of buildings.
The agency said the area was part of a now-closed industrial park where the liaison office was located.
North Korea had earlier threatened to demolish the office as it stepped up its rhetoric over Seoul’s failure to stop activists from flying propaganda leaflets across the border.
Some experts say North Korea is expressing its frustration because Seoul is unable to resume joint economic projects due to US-led sanctions.
On Saturday night, Kim Yo Jong, the influential sister of North Korea’s leader Kim Jong Un, warned that Seoul will soon witness “a tragic scene of the useless North-South liaison office (in North Korea) being completely collapsed”.
She also said North Korea’s military would have the right to take the next step of retaliation against the South.
In 2018, the rival Koreas opened their first liaison office at Kaesong to facilitate better communication and exchanges since their division at the end of the Second World War in 1945.
When the office opened, relations between the Koreas flourished after North Korea entered talks on its nuclear weapons programme.
Earlier on Tuesday, North Korea’s military threatened to move back into zones that were demilitarised under inter-Korean peace agreements.
The General Staff of the Korean People’s Army said it is reviewing a ruling party recommendation to advance into unspecified border areas that had been demilitarised under agreements with the South, which would “turn the front line into a fortress”.
While it is not immediately clear what actions North Korea’s military might take against the South, the North has threatened to abandon a bilateral military agreement struck in 2018 to reduce tensions across the border.
Inter-Korean relations began strained since the breakdown of a second summit between North Korean leader Mr Kim and US president Donald Trump in Vietnam in early 2019.
That summit fell apart because of disputes over how much sanctions should be lifted in return for Mr Kim dismantling his main nuclear complex.
Mr Kim later vowed to expand his nuclear arsenal, to introduce a new strategic weapon and to overcome the US-led sanctions, which he said “stifle” his country’s economy.