China's Defense Ministry has demanded that the US Navy end surveillance missions off the country's southern coast following a weekend confrontation between an American vessel and Chinese ships. In its first public comment on the Sunday episode, the ministry repeated earlier statements from the Foreign Ministry that the unarmed US ship was operating illegally inside China's exclusive economic zone when it was challenged by three Chinese government ships and two Chinese-flagged trawlers. "The Chinese side's carrying out of routine enforcement and safeguarding measures within its exclusive economic zone was entirely appropriate and legal," ministry spokesman Huang Xueping said in a statement faxed overnight to reporters. "We demand the United States respect our legal interests and security concerns, and take effective measures to prevent a recurrence of such incidents," Huang said. Despite the sharp remarks, Chinese Foreign Minister Yang Jiechi and US Secretary of State Hillary Rodham Clinton met in a private meeting Wednesday in Washington D.C. to say the countries agreed on the need to reduce tensions and avoid a repeat of the confrontation. But neither side yielded in their conflicting versions of events, even as they prepare for a much-anticipated first meeting between Hu and President Barack Obama at next month's G20 summit in London. The US says that Navy mapping ship USNS Impeccable was operating legally when it was harassed by Chinese boats in international waters about 75 miles (120 kilometers) off China's southern island province of Hainan. Defense Department officials say the Impeccable was on a mission to seek out threats such as submarines and was towing a sonar apparatus that scans and listens for subs, mines and torpedoes. With its numerous Chinese military installations, Hainan offers rich hunting for such surveillance. Of particular interest is the new submarine base near the resort city of Sanya that is home to the Chinese navy's most sophisticated craft. Satellite photographs of the base taken last year and posted on the Internet by the Federation of American Scientists show a submarine cave entrance and a pier, with a Chinese nuclear-powered Jin class sub docked there. While little else is known, its location on the South China Sea offers the Chinese navy access to crucial waterways through which much of the shipping bound for Japan and Northeast Asia must travel. The Hainan base shows how China is paying increasing attention to the South China Sea and other important waterways that are vital to its booming international trade and the delivery of oil and other natural resources for the expanding economy. China's nuclear submarines have up until now largely operated out of the Northern Fleet base near the port of Qingdao, said Hans M. Kristensen, the FAS researcher who first identified the Jin sub's presence from satellite photos. "The base is attaining new importance ... this is the first time a large facility in the South China Sea is being used," Kristensen said. High-seas encounters such as the Impeccable incident are likely to grow more common because China wants to assert its right to protect its secrets in the area, while the US wants to gain as much knowledge as possible about China's subs and the underwater terrain, according to maritime policy analyst Mark Valencia. "Thus such incidents are likely to be repeated and become more dangerous and they do not pertain to China and the US alone," Valencia wrote in an article posted Wednesday on the Web site of the Far Eastern Economic Review. China's claim to the entire South China Sea and its hundreds of islands and reefs overlaps with those of a half-dozen other nations, leading to occasional clashes and standoffs. Increasingly, China's rapid naval upgrade, exemplified by the Hainan base, is putting muscle behind its arguments. President and Communist Party leader Hu Jintao, who also heads the commissions overseeing the armed forces, called on the military Wednesday to pick up the pace of modernization to "resolutely safeguard the country's sovereignty, security and territorial integrity." China's territorial claims are sharpened still more by Beijing's interpretation of the United Nations Convention on the Law of the Sea. China sees the convention as giving it the right to ban a broad range of activities within its exclusive economic zone. That grates against the US position that the Navy ships were in international waters and therefore have the right to conduct surveying. Those dueling claims also lay at the heart of the last major confrontation between the two militaries, a 2001 midair collision between a Chinese fighter jet and a US spy plane in international air space south of Hainan. This time, Beijing appears to be pressing its stance even harder, citing both the UN convention and its own domestic laws and regulations.