Japan complains that Chinese coast guard vessels have sailed into its territorial waters surrounding a group of disputed islands in the East China Sea for a second time this week.
Japan's coast guard said that the four Chinese ships entered the waters around the contested islets known as the Senkaku in Japan and the Diaoyu in China at around 10:30 local time (0130 GMT) on Saturday and left the area within two hours.
A similar incident also took place on November 6, prompting Tokyo to lodge a protest with Beijing, saying the islands were “an inherent territory of Japan.”
Japan and China have been locked in a long-running dispute over the uninhabited East China Sea islands, which lie about 220 kilometers northeast of Taiwan and are believed to be rich in natural resources.
Bilateral relations soured after Tokyo nationalized part of the islands in September 2012.
Japan has made dozens of protests this year over what it says more than 30 days of intrusions by Chinese ships in the disputed waters.
The Japanese government regards the islets as a part of its territory while China maintains that it has indisputable sovereignty over them.
China is further involved in maritime disputes in the South China Sea, where several countries, including Taiwan, Brunei, Vietnam, Malaysia and the Philippines, have overlapping claims.
A Hague-based court of arbitration recently ruled in a case brought by the Philippines that China’s claims to sovereignty over the disputed areas in the South China Sea were invalid. Beijing rejected the ruling and stressed that it does not recognize the decision.