North Korea has blown up a joint liaison office used for talks between itself and South Korea, authorities in Seoul confirmed Tuesday, the latest sign that the relationship between the two longtime adversaries is rapidly deteriorating.

The four-story building is located in the town of Kaesong on the North Korean side of the demilitarized zone that divides the two countries.

North Korea has issued a number of threats against South Korea in recent days. A statement published by North Korean state media Tuesday said Pyongyang had begun an “intensive retaliatory campaign” in response to plans by a group of defectors to use balloons to send anti-North Korean leaflets north of the DMZ.

North Korea claimed the leaflets violated the deal Kim Jong Un and South Korean President Moon Jae-in struck in 2018 at their first summit, when both leaders agreed to cease “all hostile acts and eliminating their means, including broadcasting through loudspeakers and distribution of leaflets” along their shared border.

The liaison office was reopened and refurbished as part of that deal to help the two Koreas communicate.

“The recent foolish act of daring hurt the dignity of our supreme leadership,” the statement carried in KCNA read.

Kim Yo Jong, Kim Jong Un’s sister and perhaps the second-most powerful person in the country, said last week that North Korea would cut off all communication with South Korea, including a hot line meant to directly connect the leaders of the two countries, in response.

She demanded the South Korean government punish the defectors, whom she called “betrayers,” “human scum” and “riff-raff who dared hurt the absolute prestige of our Supreme Leader representing our country and its great dignity,” according to a statement carried by North Korean state news agency KCNA on Saturday.

Kim also hinted in that statement that the North Korean liaison office would be destroyed in some manner.

“Before long, a tragic scene of the useless North-South joint liaison office completely collapsed would be seen,” she said per the Saturday statement.

It’s unclear if anyone was inside the building, as Pyongyang said last week that it was completely cutting off communication with South Korea.