North Korea’s supreme leader has drawn a red line at sea, vowing to fire upon any South Korean vessel that even barely crosses it.

Kim Jong Un reportedly attended the test launch of a new surface-to-air missile on Wednesday, where he told military officials to be prepared for a strike against any South Korean ship that enters North Korea waters from now on.

The supreme leader “stressed the need for the DPRK to thoroughly defend the maritime sovereignty by force of arms and actions, not by any rhetoric, statement and public notice,” according to state-owned and operated news outlet Korean Central News Agency.

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North Korean leader Kim Jong Un attends a submarine-launched cruise missile test at an undisclosed location in North Korea in this picture released by the Korean Central News Agency earlier this year. (KCNA via REUTERS)

DPRK is an abbreviation of Democratic People’s Republic of Korea — the official name of the North Korean nation.

“He gave important instructions to bolster up military preparedness particularly in the border waters north of Yonphyong Island and Paekryong Island frequently invaded by the enemies’ warships including destroyers, escort ships and speedboats,” KCNA reported.

The Northern Limit Line (NLL) is the internationally accepted maritime line dividing North Korea and South Korea at sea — this standard border has been challenged by Kim Jong Un’s regime in the past.

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Because of Kim Jong Un’s frequent arguments that North Korean waters extend slightly farther to the south of the NLL, the exact parameters of the red line in the supreme leader’s threats are somewhat hard to understand — making the situation even more volatile.

“What is clear is that when the enemy intrudes into the maritime border recognized by us, we will regard it as an encroachment upon the sovereignty of the DPRK and an armed provocation against it,” the dictator said.

North Korean leader Kim Jong Un attends the 19th expanded political bureau meeting of the 8th Central Committee of the Workers’ Party of Korea in Pyongyang, North Korea, in this image released by the Korean Central News Agency. (KCNA via REUTERS    )

The threats make more concrete Kim Jong Un’s increasingly specific threats against South Korean officials, military, and civilians in the wake of renewed hostilities.

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In a January parliamentary meeting, the dictator told government officials, “As the southern border of our country has been clearly drawn, the illegal NLL and any other boundary can never be tolerated, and if the Republic of Korea violates even 0.001 millimeters of our territorial land, air and waters, it will be considered a war provocation.”

North Korea has continued this year its common practice of firing missiles into the ocean area between itself, its southern counterpart, and the islands of Japan.