North Korea on Tuesday said Seoul and Washington would pay a "dear price" over large-scale military exercises that started this week, urging the allies to cease "frantic war drills".

So far this year, Pyongyang has declared South Korea its "principal enemy", jettisoned agencies dedicated to reunification and outreach, and threatened war over "even 0.001 mm" of territorial infringement.

Washington and Seoul started their annual spring military exercises Monday with double the number of troops participating compared to 2023, to enhance their preparedness in responding to the ever-escalating nuclear threats from Pyongyang, they have said.

The allies said "Freedom Shield" would involve 48 field exercises and would entail missile interception drills, bombing, air assault and live-firing.

An unnamed spokesperson for the North's defence ministry urged Seoul and Washington to cease the "reckless" and "frantic war drills".

Pyongyang's military "strongly denounces the reckless military drills of the US and the ROK" and "severely warns them to stop the moves further causing provocation and instability", the spokesman said in a statement carried by Pyongyang's official Korean Central News Agency, using South Korea's official name.

The United States and South Korea "will be made to pay a dear price for their false choice while realising that it causes their security uneasiness at a serious level every moment," the spokesperson added.

North Korea has long condemned joint US-South Korea military drills, calling them rehearsals for an invasion.

It has carried out weapons tests in the past as a response to previous joint exercises of this nature.

Seoul said Tuesday its military was thoroughly prepared for North Korea's possible provocations.

"If North Korea were to directly provoke under the pretext of (our) joint military exercises, we would respond overwhelmingly according to the principle of immediate, strong, and final (action)", South Korea's defence ministry said in a statement.

Leader Kim Jong Un repeated last month 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 arch-enemy".

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.

South Korean President Yoon Suk Yeol has vowed a strong response if Pyongyang attacks, calling on his military to "act first, report later" if provoked, and saying Seoul would hit back "multiple times stronger" in the event of an attack.