Japan on Tuesday lodged a protest with China after Chinese government vessels stayed for more than half a day within what Tokyo claims as its territorial waters around a group of disputed islets in the East China Sea.
The government summoned Chinese Ambassador to Japan Cheng Yonghua Tuesday morning for the first time under Prime Minister Shinzo Abe's administration, demanding such an incident never happen again, the Foreign Ministry said in a statement.
Deputy Foreign Minister Akitaka Saiki "lodged a strong protest" with the ambassador after the four Chinese vessels passed near the Japan-administered Senkaku Islands on Monday, the ministry said.
The islands are claimed by China and Taiwan, where they are known as the Diaoyu and the Tiaoyutai, respectively.
Cheng asserted China's claims to the islands and declined to accept the Japanese demand, but the ambassador told Saiki that he would convey the message to Beijing, the ministry said.
Chief Cabinet Secretary Yoshihide Suga called the presence of the Chinese ships in the territorial waters an "extremely unusual incident and very regrettable."
In September, the Japanese government's purchase of three of the disputed islets from a private owner sparked anti-Japan protests in dozens of Chinese cities and a boycott of Japanese products.