Tokyo , Japan ( CNN ) -- The Japanese government lodged a protest with the Chinese government Monday about the alleged presence of Chinese patrol boats near disputed territory , according to Japanese media . Japanese naval authorities spotted two Chinese patrol boats late Sunday near islands that have been at the center of recent diplomatic tensions , Japan 's Kyodo News Agency reported Monday . Both countries claim sovereign rights to the islands called the Senkaku Islands in Japanese and the Diaoyu Islands in Chinese . The boats were in Japan 's `` contiguous zone '' but did not cross into Japanese territorial waters , Kyodo reported , sourcing Japan 's coast guard . But Japan 's Chief Cabinet Secretary Yoshito Sengoku said in the protest message to China that seeing Chinese patrol boats made his government feel `` uncomfortable , '' according to Kyodo . China 's foreign ministry has claimed that its boats ' patrols are both legal and based on need . Japan 's Chief Cabinet Secretary Yoshito Sengoku said Monday that Japan will step up its monitoring activities around the Islands , according to Kyodo . Japan will add six submarines to its current fleet of 16 during the next four years as it sees increased naval activity from Asian neighbor China , according to news reports from Tokyo last week . Diplomatic tensions peaked in September after Japanese authorities arrested a Chinese fishing captain near the islands and detained him for more than two weeks . The battle escalated into diplomatic threats by Beijing , the suspension of diplomatic talks and canceled trips between the nations . High level military talks between the two powers that had been suspended over the row restarted October 11 but with little talk about islands , because it was `` not very productive , '' as one Japanese defense official said . Japanese opposition politicians have called for Internet search engine Google to drop the Chinese name from its maps and were quickly joined by Japan 's foreign ministry . Anti-Japan protesters in China turned violent over a week ago , vandalizing Japanese businesses and cars . On Monday , the Chinese Embassy in Tokyo received an envelop containing a bullet and a protest document , Kyodo reported -- the second such protest this month . China and Taiwan have began aggressively challenging Japan 's claims to the islands in 2003 , according to the CIA World Factbook , as well as to surrounding seas , `` where all parties engage in hydrocarbon prospecting . ''
Chinese patrols make Japan 's government `` uncomfortable '' Japanese media reports patrols did not cross into Japanese territorial waters . The move comes as China is ramping up its military presence in the South and East China seas after a series of disputes with Japan, including an air defense zone over disputed islands that Beijing claims to