North Korea has said it will cut off all inter-Korean communication lines with the South, including a hotline between the two nations' leaders.
The North said this was the first in a series of actions, describing South Korea as "the enemy".
Daily calls, which have been made to a liaison office located in the North Korean border city of Kaesong, will cease from Tuesday.
The two states had set up the office to reduce tensions after talks in 2018.
North and South Korea are technically still at war because no peace agreement was reached when the Korean War ended in 1953.
North Korea "will completely cut off and shut down the liaison line between the authorities of the North and the South, which has been maintained through the North-South joint liaison office... from 12:00 on 9 June 2020," the Korean Central News Agency (KCNA) report said.
Military communication channels will also be cut, North Korea said.
When the liaison office was temporarily closed in January because of Covid-19 restrictions, contact between the two states was maintained by phone.
The two Koreas made two phone calls a day through the office, at 09:00 and 17:00. On Monday, the South said that for the first time in 21 months, its morning call had gone unanswered, although contact was made in the afternoon.
"We have reached a conclusion that there is no need to sit face-to-face with the south Korean authorities and there is no issue to discuss with them, as they have only aroused our dismay," KNCA said.
Kim Yo-jong, the North Korean leader's sister, threatened last week to close the office unless South Korea stopped defector groups from sending leaflets into the North.
She said the leaflet campaign was a hostile act that violated the peace agreements made during the 2018 Panmunjom summit between the South's Moon Jae-in and Kim Jong-un.
It's likely that this shut down isn't just about sending leaflets over the border - but instead, all part of a grander plan by Pyongyang.
North Korea may be creating a crisis in order to use the tension as leverage in later talks. In short, it could be simply spoiling for a fight to get attention and ask for more from its neighbour.
They've played this particular game before in 2013 to try to win more concessions from South Korea.
It's also a good distraction domestically. Kim Jong-un is failing to deliver the economic prosperity he keeps promising and rumours continue to circulate that Covid-19 is affecting parts of the country. Giving the nation a common enemy helps rally his people back around a cause.
It's worth noting one of the two signatures on this policy. Kim's sister, Kim Yo-Jong gave the order to sever ties with Seoul. This gives her a platform and the spotlight and will fuel more speculation that she is being groomed as a potential leader.
But how disappointing this must be for the Moon administration. Two years ago in a wave of optimism, the country cheered as the two leaders met and agreed to keep the phone lines open. Now all calls to the North are not being picked up.
And the question is, if this is just the start of Pyongyang's plan, what comes next?
North Korean defectors occasionally send balloons carrying leaflets critical of the communist region into the North, sometimes with supplies to entice North Koreans to pick them up.
North Koreans can only get news from state-controlled media, and most do not have access to the internet.
Ties between the North and South appeared to improve in 2018, when the leaders of both countries met three times. Such high-level meetings had not taken place in over a decade.
But Pyongyang largely cut off contact with Seoul following the collapse of a summit between Kim and US president Donald Trump in Hanoi last year that left nuclear talks at a standstill.
The two Koreas remain technically at war because the 1950-1953 Korean war ended with an armistice rather than a peace treaty.