Seoul, South Korea (CNN) — The South Korean Navy dismissed warning shots after 3 North Korean unit boats crossed a nautical limit during a Yellow Sea, an central with a South Korean Defense Ministry said.

The North Korean boats crossed into a South Korean waters during a boundary, famous as Northern Limit Line (NLL), during around 4 p.m. internal time (3 a.m. ET) on Tuesday. The ships returned to a northern side after a South Korean naval vessel dismissed 10 warning shots.

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The NLL is a de facto nautical border, that stretches from a western seashore of a peninsula into a Yellow Sea, imprinting a range between a dual neighbors. It was set by a United Nations following a Korean War though a North does not commend it.