The number of fishing boats and patrol boats from North Korea has recently surged around the Northern Limit Line. The situation has coincided with the South Korean Navy’s three-day maritime exercise in the West Sea this week.

Tension is naturally increasing as the two Koreas fought several bloody battles along the NLL across the West Sea over the past decade. Further, the timing is quite uneasy as both of the battles around the South’s Yeonpyeongdo Island in 1999 and 2002 occurred in June.

The North contests the NLL as a maritime border, as it was drawn unilaterally by the then U.S.-led U.N. Command after the end of the Korean War. The North continues to argue that the NLL should be redrawn further south.

When it comes to military readiness, the military has to prioritize Yeonpyeongdo. The North’s artillery bombardment of the island in November 2010 killed two soldiers and two civilians, injured many others, and devastated villages on the island.

It was the first attack by the North against civilians in the South since the Korean War ended in 1953. As reasons for its deadly bombing, Pyongyang cited artillery drills by the marines on the island. But it was nothing more than a thinly veiled pretext for its unwarranted aggression.

Pyongyang’s attack in 2010 was part of its tenacious efforts to invalidate the NLL, To nullify the line, the bellicose regime has provoked numerous naval clashes around the South’s five border islands of Yeonpyeong, Baengnyeong, Daecheong, Socheong and U.

Months before shelling the island, the North torpedoed the South’s Cheonan corvette near Baengnyeongdo Island, killing 46 sailors on board. It had also waged the Battle of Daecheong in 2009, near the site of the two Yeonpyeong battles.

Seriousness lies in the fact that Pyongyang has become more blatant in targeting the NLL area. In the years since the Yeonpyeong shelling, the communist country has reinforced its combat forces and firepower near the NLL, threatening to stage more destructive attacks.

The South should not rule out the possibility that all the recent moves suggest the North’s military could be plotting to raid and occupy one of the five border islands.

Further, the three smaller islands -- Daecheong, Socheong and U -- remain vulnerable to the possibility of an occupation attempt by the North, as they have only a small unit or no marine unit at all stationed on them.

Remembering the timing of the first and second Yeonpyeong armed conflicts, the military has to pay extraordinary attention to enemy movements in June.