China says island patrol has concluded BEIJING, July 16 (UPI) -- China says its fishery authorities Monday ended a weeklong patrol near a group of islands in the East China Sea that are claimed both by China and Japan. The islands incident, which last week became a diplomatic incident with Japan, involved Chinese fishing vessels. Japan said the fishing vessels had briefly entered its waters and filed a formal protest through the Chinese ambassador. China calls the islands Diaoyu Islands and Japan refers to them as Senkaku Islands. China's official Xinhua news agency said its patrol ship returned to Shanghai after its weeklong mission, along with three other vessels. Beijing says it considers the islands and affiliated islets parts of its territory since ancient times. Japan maintains the islands, historically and as a matter of international law, are an integral part of Japanese territory. Chinese fishery authorities said its patrol ships will conduct further missions after a short break but gave no details. The islands issue heated up after recent reports the Japanese government plans to nationalize the uninhabited islands by purchasing parts of them from their Japanese owner. Japan's Kyodo News has quoted a U.S. State Department official as saying the islands fall within the scope of the 1960 Japan-U.S. security treaty, which requires the United States to defend Japan in the event of armed attack. Separately, the China Daily, quoting analysts, accused Japan Tuesday of sensationalizing the islands issue, warning it will stir up nationalism within the country and help more right-wing politicians win seats in parliament, thus straining China-Japan ties. The report said Japanese Ambassador Uichiro Niwa, who had been called to Tokyo, returned to Beijing Monday but the Japanese Embassy declined to say whether or when he would communicate with China. Ruan Zongze with the China Institute of International Studies told China Daily the seabed around the islands is rich in natural resources. The islands may serve as a strategic shield for Japan and "the islands' geopolitical value outweighs the importance of the oil and gas buried in the region," he said. The newspaper said reports released in the late 1960s pointed to the possibility of rich undersea oil and gas resources in the East China Sea beneath the islands in dispute.