North Korea has said it will send soldiers to closed inter-Korean co-operation sites in its territory and reinstall guard posts and resume military exercises at frontline areas, nullifying deals reached with South Korea two years ago.
The announcement is the latest in a series provocations by North Korea in what experts believe are calculated moves to apply pressure on Seoul and Washington amid stalled nuclear negotiations.
On Tuesday, the North destroyed an empty inter-Korean liaison office in its territory.
North Korea's recent actions have not lead to clashes or bloodshed, but they still raise animosity on the peninsula to a level unseen since Pyongyang entered nuclear talks in 2018.
The North's General Staff said military units will be deployed to the Diamond Mountain resort and the Kaesong industrial complex, both just north of the heavily fortified border.
The two sites, built with South Korean financing, have been closed for years due to inter-Korean disputes and US-led sanctions.
The North also said it will resume military exercises, re-establish guard posts and boost military readiness in border areas as well as open frontline sites for flying propaganda balloons towards South Korea.
Those steps would reverse agreements reached between the Koreas in September 2018 aimed at lowering military tensions along the border.
South Korea's military expressed regret over the North Korean announcement and warned that the North will face unspecified consequences if it violates the 2018 deals.
Major General Jeon Dong Jin of the Joint Chiefs of Staff told reporters that Seoul maintains military readiness and will strive to prevent military tensions from rising.
Vice unification minister Suh Ho warned against destroying South Korean assets that remain at the two co-operation sites.
Under the 2018 agreements, both Koreas halted live-firing exercises, removed some land mines and destroyed guard posts along the world's most heavily armed border.
Some analysts see North Korea's provocations as an attempt to get concessions from Washington and Seoul at a time when its economy, already battered by sanctions, is likely to have worsened due to the coronavirus pandemic.
They say North Korea may be frustrated because the sanctions prevent Seoul from breaking away from Washington to resume joint economic projects with Pyongyang.
The North's official Korean Central News Agency on Wednesday said that recent actions were taken to retaliate for South Korea's failure to prevent activists from floating propaganda leaflets across the border.
It said the destruction of the building was a "reflection of the zeal of our enraged people to punish human scum who challenged the noblest dignity and prestige of our country and those who sheltered the scum, perpetrators of shuddering crime".
Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, separately revealed that Pyongyang had rebuffed a recent offer by South Korean President Moon Jae-in to send special envoys to Pyongyang to defuse tension.
Ms Kim, who has spearheaded the North's recent rhetoric against South Korea, called Mr Moon's offer a "petty farce" and a "trick" to tide over a crisis.
One of Mr Moon's senior presidential advisers, Yoon Do-han, called Ms Kim's statement "very rude", "irrational" and "senseless", and warned that South Korea will not tolerate similar statements by North Korea any longer.