North Korea destroyed an inter-Korean liaison office on its territory on Tuesday, as a row over a propaganda leafleting campaign against the Pyongyang regime reached fever pitch.
The demolition occurred at 14:50 local time.
"The liaison office was tragically ruined with a terrific explosion," read a statement from the Korean Central News Agency, a North Korean government mouthpiece.
It said the demolition was a continuation in the process of cutting off ties to South Korea, "corresponding to the mindset of the enraged people to surely force human scum and those who have sheltered the scum to pay dearly for their crimes."
South Korean news agency Yonhap released images of a column of smoke rising from the site of the former office. The South Korean Defence Ministry confirmed the demolition.
Tensions have escalated between the neighbours in recent weeks, following a propaganda airdrop campaign against North Korean leader Kim Jong Un carried out by activists in South Korea, who have sent leaflets denouncing him across the border, carried by balloon. The groups sent about a half million across the border in one action at the end of May.
Pyongyang said the campaign is a sign that Seoul is tolerating the actions of North Korean refugees active at the border, even though Seoul has urged the activists to stop, warning them they are exacerbating tensions.
Kim's younger sister, Kim Yo Jong, had threatened that North Korea would take revenge and should "surely break with" South Korea, after Pyongyang accused Seoul of having done nothing to address the campaign. She had also at one point urged for the "useless" station in Kaesong to be torn down.
North Korea had already stopped answering calls at the station to protest.
Another threat - so far not carried out - calls for the North to pull out of a bilateral 2018 military agreement with the South.
"Our army is keeping a close watch on the current situation, in which the North-South relations are turning worse and worse, and getting itself fully ready for providing a sure military guarantee to any external measures to be taken by the party and government," read a statement from the Korean Central News Agency.
North and South Korea have never formally ended the 1950s-era war that saw the creation of the two rivals. The current South Korean government has put significant weight on efforts to improve relations, which were helped along with three meetings between Kim and US President Donald Trump in 2018 and 2019.
There were similar high-profile meetings between the leaders of the two Koreas, one of which saw Kim and South Korean President Moon Jae In symbolically walk across the border together, hand in hand.
However, there has been little in the way of solid improvements in the relationship. North Korea has also indicated it has no intention of acceding to key demands, such as giving up its nuclear ambitions.
The Kaesong site was one of the few tangible steps taken by the two countries as part of the strengthening of ties. It was supposed to be a site for discussing bilateral relations and - eventually, Seoul hoped - talks about ending Pyongyang's nuclear programme.
But it had gone unused in recent months.
Return to negotiating table
Moon had pleaded just a day before for Pyongyang to return to the negotiating table.
The destruction, in turn, drew its own sharp warning from Seoul.
"If North Korea takes further steps to escalate the situation, then we will react very sternly," read a statement from the president's office.
Korea experts say Pyongyang's latest move is an effort to drive a wedge between South Korea and the United States.
"This is North Korea seeking to manufacture tension. Pyongyang is suffering under stinging sanctions and is trying to corner Seoul into breaking with the US-led sanctions campaign," wrote Korea expert Jean H Lee from the Wilson Center, based in America.
Tuesday's action followed recent threats to reintroduce troops to the demilitarized zone between the countries, including in Kaesong, where the two countries jointly operated an industrial zone between 2004 and 2016.
China, North Korea's main backer, made a call for stability after the incident.
Foreign Ministry spokesperson Zhao Lijian told a press briefing on Tuesday that "North Korea and South Korea are one people and, as a neighbour, China has always hoped for the preservation of peace and stability on the Korean Peninsula."