South Korea's president vowed Tuesday to defend a string of islets against Japanese claims in Seoul's strongest criticism yet of Tokyo in the long-running territorial dispute.

The islets — known as Dokdo in Korean and Takeshima in Japanese — are under South Korean control. The dispute flared anew this month when Japan said it would conduct a maritime survey in waters surrounding the islets.

The waters lie halfway between the countries. The area, claimed by both countries, is a rich fishing ground and is also believed to have methane hydrate deposits, a potential source of natural gas.

After negotiations in Seoul, Japan agreed on Saturday to cancel the survey as long as South Korea delays its move to officially register the Korean names in the area.

President Roh Moo-hyun told the nation on television Tuesday it was South Korea's "given right" to register the Korean names.

Roh called Tokyo's territorial claim "an act that denies Korea's complete liberation and independence."

"We will never tolerate this," Roh said.

It was the strongest criticism of Japan yet from South Korea, which harbors deep bitterness toward Japan for its 1910-45 colonial rule of the Korean Peninsula.

"We will react strongly and sternly against any physical provocation," Roh said. "This is a problem that can never be given up or negotiated, no matter at what cost or sacrifice."

South Korea vehemently opposes Japan's survey plans and this month dispatched 20 gunboats to the area, warning of a possible physical confrontation if Japan proceeded.

Japan has maintained it has the right to conduct the survey under international law, but kept its two unarmed survey ships out of the waters.

Tokyo maintains the survey is needed to match South Korean efforts to map the sea floor and name underwater formations, including basins and ridges.

In addition to the islet feud, the two sides are at odds over Japanese Prime Minister Junichiro Koizumi's repeated visits to a Tokyo war shrine along with school textbooks that critics say gloss over the country's past abuses.