North Korea has blown up a joint liaison office with the South as tensions between the two countries continue to rise.
The demolition of the building in the border town of Kaesong in North Korea came just hours after the North's military threatened to move back into demilitarised zones along the border.
South Korea's National Security Council said the attack "abandons the hopes of everyone who wanted the development of inter-Korean relations and peace settlement in the Korean Peninsula".
The South also expressed "strong regret" over the incident and warned it will "respond strongly" if North Korea "continues to worsen the situation".
No South Koreans were working in the building at the time which is largely symbolic.
North Korea's state-run Korean Central News Agency claimed the building was destroyed in a "terrific explosion" because it reflects "the mindset of the enraged people to surely force human scum, and those who have sheltered the scum, to pay dearly for their crimes”.
The increase of tensions between the North and South follows the North's stalled nuclear talks with the US and threats from its military.
Last weekend, the North Korean leader's sister, Kim Yo-Jong, warned the South it will see the collapse of the "useless" inter-Korean liaison office.
While last week, the North announced it would cut all government and military communication channels with the South after it failed to stop activists floating anti-Pyongyang leaflets across the border.
The North has threatened to leave a 2018 bilateral tension-reduction agreement - sparking concerns among experts that it could trigger clashes along land and sea borders.
On Monday, South Korean President Moon Jae-in called on North Korea to stop the hostility and return to talks.
He said the two countries must not reverse the peace deals agreed in 2018.
Cover image: Smoke rises from the inter-Korean office in Kaesong following the demolition (Picture: Yonhap/PA).