South Korean Defense Ministry officials report that North Korean patrol craft violated the Northern Limit Line (NLL) last Saturday, for a total of three violations this year, resulting in the South Korean Navy being put on alert.

The violations could be deliberate attempts by the North Korean regime to signal displeasure with the new Lee Myung-bak administration in the Republic of Korea (ROK), or simply mistakes by the North Korean patrols; it’s hard to tell. But in an era when official North Korean publications are scoured for minute changes in tone and verbiage in order to determine subtle shifts in Kim Jong-il’s thinking, someone is sure to read intent into every action taken.

An extension of the Military Demarcation Line (MDL), the NLL (북방한계선 / 北方限界線) is the maritime demarcation line in the Yellow Sea (West Sea) between North and South Korea, established by the U.S.-led United Nations forces in August 1953 after negotiations with North Korea failed to reach an agreement on the issue. The NLL is not included in the 1953 armistice (DOC) and is not recognized by North Korea. Six South Korean sailors died in a June 2002 naval skirmish with North Korean patrol vessels that had crossed the NLL.

The blue line above is the NLL, which is the de facto maritime border. The North Korean claimed maritime boundary (북쪽주장해상경계선) is the red line (with the exception of the islands cut out), however North Korean vessels do not defend it. Even though North Korea claims the islands the red line goes around, they are held by South Korea, or at least not controlled by the North.