The Ministry of Foreign Affairs said yesterday it had asked its representatives in Tokyo to express their serious concerns to the government there about the a landing by Japanese right-wingers on the disputed Tiaoyutai islands in the East China Sea.
Nine members of Nihon Seinensya (Japan Youth Society) landed on the uninhabited, rocky islet at 7:04am and stayed there for about five hours, according to Japan's coast guard.
"The members, all men ... said they needed to do maintenance work on a lighthouse on the Uotsuri Island," the official said.
Taiwan's foreign ministry restated Taiwan's claims to ownership of the islands and protested to the Japanese government against the landing. It demanded the Japanese government prevent similar incidents from happening again.
The Nihon Seinensya built the lighthouse in 1978 and it needs to have the batteries replaced this year, the group said on its Web site.
They chartered a fishing vessel at Ishigaki Island, some 160km to the south of the disputed islet, and departed late Sunday, the coast guard said.
They reached the island using a rubber dinghy. The Japan Coast Guard sent several vessels to monitor the rightists' voyage but declined to specify how many ships were involved.
"We had been instructing them not to land on the island without approval from the state but they did not listen," the coast guard official said.
Japan declared the islands as part of its territory in 1895 and they were temporarily put under US control after World War II. They were returned to Japanese rule in 1972.
The island chain is claimed by Japan, China and Taiwan.
The simmering territorial dispute came to the fore in the early 1970s, when China and Taiwan made their claims to the islands after oil deposits were confirmed in the area by a UN agency.