Japanese and South Korean negotiators raced Thursday to avert a clash over disputed islets as Seoul accused Tokyo of imperialistic ambitions and warned of a possible confrontation at sea.

Behind-the-scenes talks on a diplomatic solution came as tensions mounted over a Japanese plan to survey resource-rich waters near the islands, which are occupied by South Korea but claimed by Japan.

Some 20 South Korean gunboats have been dispatched to the area in anticipation of the arrival of Japanese survey ships. The gunboats were scheduled to conduct high seas seizure drills Thursday, but delayed the exercises due to bad weather.

In Seoul, the Foreign Ministry summoned the Japanese embassy for talks, while warning of the possibility of a clash. Japan held the "key" to preventing conflict, ministry spokesman Choo Kyu-ho said.

President Roh Moo-hyun accused Tokyo of harboring imperialistic ambitions. Many South Koreans say the basis of Japan's claim is its 1910-45 colonial rule of the Korean Peninsula.

"There are some people claiming territorial rights to former colonies that were once acquired through a war of aggression," Roh said in a speech at a breakfast prayer meeting of Christian leaders in Seoul.

"We are now in a difficult situation," he said. "Problems cannot be solved just by goodwill."

The rocky outcroppings, called Dokdo by Koreans and Takeshima in Japan, are surrounded by rich fishing waters and both countries claim the area as part of their exclusive economic zones. Korea Gas Corp. estimates the area also has enough methane hydrate deposits to meet South Korean natural gas demands for 30 years.

In Tokyo, Chief Cabinet Secretary Shinzo Abe said there had been "unofficial" contact between the two sides but Japan still planned to go ahead with the survey.

"The Japanese Coast Guard is carrying out preparations to conduct a maritime survey that is based on international law," he said. "A calm response is necessary, and unofficial contacts between Japan and South Korea are taking place."

The European Union called for a peaceful resolution.

"The EU is saddened to see that there are tensions between the two countries and hopes that the countries can find a peaceful diplomatic solution," visiting EU Commissioner for External Relations Benita Ferrero-Waldner told a news conference in Seoul.

Meanwhile, hundreds of riot police guarded the Japanese Embassy in Seoul as demonstrators gathered, chanting "Dokdo is our territory!" A dozen fishery workers later failed in an attempt to storm the compound.

Prime Minister Junichiro Koizumi suggested Japan may dispatch a foreign ministry official to South Korea to avert a clash. News reports had earlier said Undersecretary for Foreign Affairs Shotaro Yachi may travel to Seoul as early as Friday.

When asked about the reports, Koizumi said Japan would do its utmost to reach an amicable solution.

News reports said the survey might begin later Thursday. Two survey ships left Japan's west coast on Wednesday but have been lingering offshore since.

Foreign Minister Taro Aso said Thursday Japan needs to conduct the survey to protect its national interests.

But Japanese newspapers reported Thursday that Tokyo offered to drop its survey if Seoul agreed to not register Korean place names in the disputed waters, including a proposal to rename the Sea of Japan, at an international conference in June. Some undersea basins and ridges are not yet named.

Song Min-soon, Roh's security adviser, said in an interview with South Korea's KBS Radio, however, that Seoul has no intention to withdraw its renaming proposal.

The leader of South Korea's ruling Uri Party, meanwhile, urged tougher measures against Japan.

"Japan has finally crossed the line," Chung Dong-young was quoted as saying by party spokeswoman Seo Young-kyo. "We have been practicing somewhat quiet and calm diplomacy up until now, but we can no longer stand this."

The island dispute marks a further deterioration in ties between the two countries, which have struggled for years to overcome a centuries-long history of animosity.

The countries are also at odds over Koizumi's repeated visits to a war shrine that critics, Seoul included, consider a glorification of Japan's imperialist past.