TOKYO- The Japanese government is on higher alert after a series of incursions into Japanese territorial waters by Chinese ships, including in areas that had previously been free from such problems.   In addition to waters around the Japanese-administered Senkaku Islands in Okinawa Prefecture, southern Japan, Chinese coast guard ships have recently been spotted in Japanese waters off the Kyushu southwestern region and around the Tsugaru Strait in northeastern Japan for the first time.

Worried that China may step up its maritime expansion further, the Japanese government plans to call for self-restraint, officials said.

On July 2, a surveillance ship of the Chinese Navy entered Japanese waters in the Tsugaru Strait.

A Chinese coast guard vessel sailed into Japanese waters off Tsushima Island, Nagasaki Prefecture, in the Kyushu region, on July 15, and it was spotted with another ship in Japanese waters off Okinoshima, an island in nearby Fukuoka Prefecture, later in the day. Furthermore, the two ships entered Japanese waters in the Tsugaru Strait last Monday.

China informed Japan in advance of the passage of the coast guard ships in the Tsugaru Strait from the Sea of Japan, explaining that they were to take part in fisheries patrols in the northern Pacific Ocean, a Japanese official said.

The official showed distrust in China, saying, "They (the ships) could take a route in the high seas to reach the northern Pacific, but they purposely sailed in Japanese waters."

Under the UN Convention on the Law of the Sea, ships of all states have the right of innocent passage in others' territorial waters, without infringing on the peace and security of the coastal states. Therefore, the Japanese government has stopped short of filing an immediate protest and has instead informed China of its interest in the passage through the territorial waters in an attempt to find out the intentions behind these activities.

Some in the Japanese government suspect that the latest incursions represent retaliation by China against Japan for its support for the United States' Freedom of Navigation operations in the South China Sea, where China has been showing maritime assertiveness.

In the meantime, entry by Chinese ships to Japanese territorial waters around the uninhabited Senkaku Islands continues, totaling 19 times this year as of last Monday. China claims the islands as its own, calling them Diaoyu.

At a summit meeting in Germany on July 8, Japanese Prime Minister Shinzo Abe and Chinese President Xi Jinping agreed to make efforts to improve relations between their countries, which have often been strained over historical and territorial issues. Bilateral tensions at sea have few signs of easing, however. (Jiji Press)