Pyongyang, North Korea - North Korea on Sunday accused the US and South Korea of conducting more aerial espionage around the peninsula, warning it would take "immediate action" if its sovereignty was breached.

America has deployed dozens of military planes "in air espionage against the DPRK from May 13 to 24," the North's vice defense minister Kim Kang Il said in a statement, referring to his country by its official name.

The espionage activities observed over the 12-day time frame were "at a level beyond the wartime situation," he said in the statement, which was carried by the official Korean Central News Agency.

"Such hostile military espionage, together with various military drills, has become the root cause of ever-escalating regional military tensions," he added.

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The official also lashed out at the South Korean navy for what he called "enemy intrusion across our maritime border," claiming such acts were conducted under the guise of "mobile patrols."

The vice minister said the North's military would "take necessary military measures," adding: "Dangerous consequences will ensue from such frequent intrusions across our maritime border."

He also targeted the sending of balloons containing anti-regime leaflets by South Korean civic groups across the border, calling it a "dangerous provocation" and warning of "tit-for-tat action."

Despite a ban that took effect in 2021, South Korean activists have for years flown balloons containing propaganda leaflets and US dollars over the border, a tactic against which Pyongyang has long protested.

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Inter-Korean relations are at one of their lowest points in years, with Pyongyang declaring Seoul its "principal enemy."

It has dismantled agencies dedicated to reunification and threatened war over "even 0.001 mm" of territorial infringement.

South Korea and its key security ally America routinely conduct joint military drills, which they say are necessary to guard against growing threats from the nuclear-armed North.

Pyongyang regards all such drills as rehearsals for invasion, and has been known to conduct weapons tests and live-fire counter-drills in response.