South Korea on Monday said a submerged outcropping of rock off its southern coast was part of its "natural territory", days after a top Chinese official reportedly laid claim to the disputed area.

Ieodo -- a reef about five metres (16.4 feet) underwater -- lies within the overlapping exclusive economic zones of South Korea and China and for years has been a source of diplomatic strain between both nations.

President Lee Myung-Bak called the area a "natural South Korean territory by any measure", saying it was closer to South Korea's southernmost island of Marado than to the nearest Chinese island by about 100 kilometres.

"Chinese government will know, based on common sense, that Ieodo belongs to South Korea," Lee told reporters, adding that years of bilateral negotiations to reach agreement yielded little progress.

Lee's comment came after Liu Cigui, the chief of China's State Oceanic Administration, said that Ieodo was in waters under Chinese control and should be patrolled by Chinese vessels and aircraft, according to media reports.

South Korea's Deputy Foreign Minister Kim Jae-Shin summoned Chinese Ambassador Zhang Xinsen Monday to lodge a protest against Liu's comments, ministry officials said.

Beijing's renewed claim to the area is being seen as a way to get an upper hand in future negotiations with Seoul over maritime territory, analysts say.

Lee warned any disputes in the resource-rich area -- Seoul's major sea trade route -- could cause a serious setback to the country's trade-driven economy.

South Korea in 2003 tried to reinforce its control over the disputed area by building a maritime research station there despite Beijing's opposition.