"First of all, this type of activity, based on a legally unjustified capture [of islands], does not coincide with Japan's position and causes deep regret. Through diplomatic channels, we have reported the position of our country to Russia and China and have lodged a protest," Suga said at a press conference in Tokyo on Monday.
He explained that the protest had been issued by the Japanese Embassy in Russia to the Russian Foreign Ministry on June 7.
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It is important to solve the problem of the disputed islands, the official stressed.
"The Japanese government will continue to persist in negotiating with Russia regarding a solution to the problem of the ownership of the four northern islands and the conclusion of a peace treaty," Suga said.
On June 5, Russia notified Japan of its intention to begin laying an underwater fiber-optic cable from Sakhalin towards the southern Kurils on June 10. A large Chinese firm is acting as a partner for the Russian side.
Russo-Japanese relations have long been complicated by the fact that the two nations never signed a permanent peace treaty after the end of World War II. A deal was not reached because of a disagreement over a group of four islands that are claimed by both countries — Iturup, Kunashir, Shikotan, and Habomai — collectively referred to as the southern Kurils by Russia, and Northern Territories by Japan.