South Korea's military warned Wednesday it will make sure that North Korea "pays the price" if it actually takes military action against the South.

The Joint Chiefs of Staff statement came hours after North Korea said it will redeploy troops to an inter-Korean industrial park in the western border town of Kaesong and the Mount Kumgang joint tourism zone on the east coast.

The North also said it will restore guard posts removed from the Demilitarized Zone separating the two sides and resume all kinds of regular military exercises near the inter-Korean border in an apparent move to abolish a military tension-reduction deal signed in 2018.

"These moves thwart two decades of efforts by South and North Korea to improve inter-Korean relations and to keep peace on the Korean Peninsula. If the North actually takes such a move, it will certainly pay the price for it," Jeon Dong-jin, director of operations at the Joint Chiefs of Staff, said.

Earlier, North Korean leader Kim Jong-un's powerful sister, Kim Yo-jong, threatened to scrap the deal altogether in anger over anti-Pyongyang leaflets sent across the border by activists here.

The younger Kim said Seoul should get ready for the "scrapping of the North-South agreement in military field which is hardly of any value" if it fails to take corresponding steps for the leaflet campaigns.

After a series of statements ratcheting up tensions on the peninsula, the North blew up an inter-Koran joint liaison office in the western border town of Kaesong on Tuesday.

"Regarding the current security situation, our military is closely monitoring the North Korean military moves round-the-clock and maintains a staunch readiness posture. We will continue to make efforts to manage the situation stably to prevent this from escalating into a military crisis," Jeon said. 

As North Korea upgraded its guard duty level to "top class combat duty system" for front-line troops, the South Korean and US authorities have also beefed up their surveillance and readiness posture, according to JCS officers.

It is the first time since 2013 that North Korea said it heightened the alert to the highest level, which means that troops are in full gear to be ready for combat operations.

South Korea has been operating such assets as ballistic missile early warning radar and Aegis-equipped destroyers, and the US flew EP-3E and RC-12X surveillance aircraft on an apparent mission to monitor the North, according to sources. 

"No unusual movements have been detected as of now. But we have been in a full posture against any eventualities," a JCS officer said.(Yonhap)