A Japan Coast Guard patrol ship sails around while the city government of Tokyo's survey staff, on a boat, conduct surveys around a group of disputed islands known as Senkaku in Japan and Diaoyu in China in the East China Sea, Sunday. — ReutersABOARD THE KOYO MARU — Tokyo city officials planning to buy tiny islands at the center of a longtime territorial dispute with China surveyed the area Sunday on a visit meant to send a message of ownership. The boat, carrying 25 experts and officials as well as journalists from news organizations including The Associated Press, circled the five uninhabited islands in the East China Sea which are controlled by Japan but also claimed by China and Taiwan. China responded quickly to the survey, saying any unilateral action by Japan on the islands is “illegal" and “invalid." Tokyo city officials say the survey is crucial and includes measuring the water depth to build a dock at the islands, known as Senkaku in Japan and Diaoyu in China. Japan's central government did not grant permission to land on the islands. Tokyo Gov. Shintaro Ishihara, a strong nationalist, has raised 1.45 billion yen ($19 million) in private donations over the last several months to buy the islands from the Japanese family that owns them. Supporters think having the government own the islands will strengthen Japan's control over them and send a tougher message to China. “It is an undeniable fact that the islands are Japanese territory, so our task is to see how we can best maintain that," Yoshihiko Yamada, a special adviser to the city's team, said aboard the boat. The team was scheduled to study the islands for about 10 hours Sunday before heading back to Okinawa in southwestern Japan. The islands, a symbol of patriotic pride for some people in China and Japan, are near key sea lanes and are surrounded by rich fishing grounds and untapped natural resources. China's Foreign Ministry said it had already made “solemn representations" to Japan about the visit. “The Chinese side reiterates that any unilateral action by the Japanese side on the Diaoyu islands is illegal, invalid, and will not change the reality that the Diaoyu islands and its affiliated islands belong to Chinese territory," it said in a statement. — AP