President Lee Myung-bak visited Yeonpyeong Island on Thursday, becoming the first South Korean leader to set foot on the frontline island in the West Sea near North Korea.

The island is just 1.5 km from the Northern Limit Line, the de facto maritime border, and only 3 km away from North Korea's Sok Island.

President Lee Myung-bak looks around the ruins of a house that was hit during the North Korean attack on Yeonpyeong Island in 2010, during his visit to the island on Thursday. /Yonhap

"Our military should stake their lives on safeguarding the NLL until unification comes. That is the very way to ensure peace," said Lee, dressed in a fatigue jacket, at lunch with Marines and residents on the island.

"Safeguarding the line... also protects the lives and safety of our people. We must defend the NLL," he said.

Lee added that North Korea is in a dismal economic state but continues to threaten South Korea and the entire world by making nuclear weapons. If the North scrapped its nuclear development program, it would be able to use that money to feed its people, he said.