"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.
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.