SEOUL — The frequency of recent incursions by North Korean fishing boats into South Korean-controlled waters suggests they might have been intentional, possibly as a provocation amid tensions on the peninsula, South Korean officials said Monday.

“It’s a little hard to consider it as a simple mistake because too many ships have crossed the Northern Limit Line too many times,” Unification Minister Yu Woo-ik told reporters at a media luncheon. “That is why the (South Korean) government at this point is closely observing the situation.”

South Korean patrol boats fired warning shots at six North Korean fishing boats around 3:20 p.m. Friday after they strayed across the maritime border near the South’s Yeonpyeong Island. The fishing boats immediately returned to Northern waters, and no injuries or deaths were reported, according to the Ministry of National Defense.

The North’s Korean Central News Agency later posted a statement on its website claiming that South Korean naval vessels entered and fired on fishing boats in North Korean waters on Sept. 21.

According to the MND, fishing boats also crossed into South Korean waters on Sept. 12, 14, 15 and 20. The spokesman denied that any North Korean fishing boats crossed the line Saturday, as some South Korean media reported.

Yu said he hoped the North did not intend the fishing boat crossings as a provocation. He blamed the current status of relations between the two countries — which he described as “stagnant” and “difficult” — on previous North Korean military attacks.

The communist North shelled Yeonpyeong Island in November 2010, leaving four people dead, including two civilians. In March 2010, the North torpedoed a South Korean warship, the Cheonan, while on patrol in the Yellow Sea, killing 46 servicemembers.

Reclusive North Korea claims the demarcation line, established at the end of the Korean War, was unfairly drawn too far north.

South Korean President Lee Myung-bak addressed growing concern Monday about sea provocations with the North, saying in a speech to mark the anniversary of the founding of the Coast Guard that “threats to our waters have been increasing day by day,” Yonhap News reported.

“We can never let our guard down even for a moment as North Korea continues to threaten maritime provocations, and tensions in Northeast Asian waters are escalating,” Lee said, according to Yonhap.

Yu said that “on outside appearance, the power succession in North Korea seems to have been smoothly completed.” But he also said Kim Jong Un is likely still trying to stabilize his power base after taking over last December following the death of his father, Kim Jong Il.

“Because North Korea has closed off relations with the outside community and it is suffering from many economic hardships, I believe there are some kinds of limitations in trying to stabilize its power,” Yu said.

Yu said he expects the next South Korean administration to maintain the country’s unification policies after presidential elections later this year. Unification policies are moving from a “single track system” focused on increasing exchange and cooperation between the two Koreas to a “multiple track system” focused on unification preparations, he said.

Yoo Kyong Chang contributed to this story.

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