South Korea's ruling party chairman visits islets in dispute with Japan(Updated 04:02 p.m.)

South Korea's ruling party chairman made a surprise visit to a string of disputed islets Monday and said the country must defend them at any cost, amid heightened tensions with Japan over rival claims to the territory.

Chung Dong-young's visit came as a top Japanese diplomat was set to arrive in South Korea to try to repair bilateral ties battered by recent spats over the islets, known as Dokdo in Korean and Takeshima in Japanese.

Japan's Senior Vice Foreign Minister for Foreign Affairs Yasuhisa Shiozaki was scheduled to meet South Korean Foreign Minister Ban Ki-moon later Monday.

Chung, a former unification minister, warned that Japanese moves to deny South Korea's sovereignty over the islets would bring unhappy results to both sides, and that Japan will be held responsible.

"Dokdo cannot be the subject of any negotiation or dispute," Chung said on his one-day trip to the islets, according to a transcript provided by the Uri Party.

"We will regard all sorts of provocations, including an attempt to make our land Dokdo a dispute, as an act of aggression against the Republic of Korea and will deal sternly with it." The Republic of Korea is the official name of South Korea.

The islets are currently under South Korean control, but are also claimed by Japan. The long-running dispute over the territory flared anew last month when Japan said it would conduct a maritime survey in waters surrounding the islets.

After negotiations in Seoul, Japan agreed to cancel the survey if South Korea delayed its plans to officially register Korean names for underwater physical features in the area. Negotiators were expected to meet this month to talk about demarcating their maritime boundaries.

Last week, South Korean President Roh Moo-hyun vowed to defend the outcroppings at all costs, prompting Japan to accuse South Korea of occupying the islets illegally.

Since the 1950s, the outcroppings have been inhabited by a small South Korean police detachment. The area is a rich fishing ground and is also believed to have methane hydrate deposits, a potential source of natural gas.