Japan lodged a protest "repeatedly" with Beijing over Chinese vessels spotted daily in recent months near a group of uninhabited islets in the East China Sea, Foreign Minister Toshimitsu Motegi said on Tuesday.
The minister's words come hours after the Japan Coast Guard urged four Chinese ships not to approach what Tokyo considers to be its territorial waters near the Japanese-administered Senkaku Islands, a source of diplomatic tensions.
The incident was "extremely regrettable," Motegi told a news conference. "We have made a serious protest [to China] repeatedly through diplomatic channels."
"We cannot restore a genuine diplomatic relationship [with China] without stability in the East China Sea," he said.
China and Taiwan also claim the islets, where they are known as Diaoyu and Tiaoyutai, respectively.
Meanwhile, Ishigaki city council in Japan's Okinawa prefecture approved legislation on Monday to change the name of an administrative area covering the islets from "Tonoshiro" to "Tonoshiro Senkaku," immediately drawing harsh criticism from Beijing.
The city's "adoption of the so-called name-changing bill is serious provocation against China's territorial sovereignty, which is illegal, null and void. It cannot change the fact whatsoever that Diaoyu belongs to China," China's Foreign Ministry spokesman Zhao Lijian told reporters on Monday.
Taiwan called on Japan to exercise self-restraint in order not to undermine bilateral ties as well as peace and stability in the East China Sea, Kyodo News reported.
