South Korean President Lee Myung-bak made a surprise visit to a front-line island near the tense western sea border with North Korea on Thursday, the scene of a deadly artillery attack by the communist nation two years ago.

It is the first time that Lee has visited the island of Yeonpyeong near the Yellow Sea border with the North. The island was bombarded in the North's shelling attack in November 2010, leaving two South Korean Marines and two civilians dead.

Officials said the visit was aimed at checking on military vigilance in the front-line area.

The visit also came amid allegations that Lee's liberal predecessor, late former President Roh Moo-hyun, said during his 2007 summit with then North Korean leader Kim Jong-il that Seoul would not insist on the sea border that Pyongyang does not recognize.

The allegations, raised by a ruling party lawmaker earlier this month, are believed to be targeted at the opposition Democratic United Party's presidential candidate, Moon Jae-in, who served as chief of staff to Roh at the time.

North Korea has never recognized the maritime boundary, known as the Northern Limit Line (NLL), which was drawn unilaterally by the U.S.-led United Nations Command when the 1950-53 Korean War ended, and demands that the line be drawn further south.

Areas near the border have been the scene of a number of bloody inter-Korean clashes. The two sides fought naval gun-battles in the area in 1999, 2002 and 2009. The North also torpedoed and sank a South Korean warship in the area in March 2010, killing 46 sailors. (Yonhap News)