Nuclear-armed North Korea has this year declared South Korea its "principal enemy", closed agencies dedicated to reunification and outreach, and threatened war over "even 0.001 millimetres" of territorial infringement.

Leader Kim Jong Un repeated on Friday that Pyongyang would not hesitate to "put an end" to South Korea if attacked, calling Seoul the North's "most dangerous and first enemy state and invariable archenemy".

The hawkish Yoon has bolstered defence cooperation with the United States and Japan since coming to office in 2022, including expanding joint drills, to counter Pyongyang's growing threats.

"If the enemy provokes us, adhere to the principle of 'act first, report later' and respond decisively and overwhelmingly without hesitation to completely shatter the enemy's will," Yoon said during a visit to a front-line Republic of Korea Marines Corps unit, according to his office.

Yoon made similar remarks last month and during a visit to a frontline army unit in December.

He also inspected a multiple-launch strike system on Saturday, Lunar New Year, and stressed the need to be "fully prepared to respond immediately in case of enemy provocation".

As well as an increase in rhetoric, both sides have ramped up frontier security in recent months and conducted live-fire drills along their shared border.

In January, North Korea fired an artillery barrage near two South Korean border islands, prompting a live-fire drill by the South and evacuation orders for residents.

Yoon said last week the "irrational" North Korean government was likely to carry out multiple provocations, including cyberattacks and drone intrusions, ahead of the South's election on April 10.

Yoon, who came to office vowing to get tough on Pyongyang, and his conservative party are aiming to regain a parliamentary majority for the first time since 2016.

North Korea has a long track record of provocations ahead of South Korean elections, experts say, part of its broader strategy to cause disruption south of the border.