The Foreign Ministry said Tuesday it has filed a protest with Nippon Television Network Corp. after the chief of the Moscow bureau of an affiliated broadcaster used a Russian visa to visit Etorofu Island, one of four Russian-held islands off Hokkaido.
The ministry said it has confirmed that the bureau chief entered Etorofu last Saturday with a Russian visa and described the act as "being extremely regrettable."
The bureau chief landed according to Russian immigration procedures, undermining Japan's claim that it has sovereignty over the island, the ministry said, adding it has strongly requested NTV to take preventive measures.
A news program aired by NTV on Tuesday night featured the bureau chief's visit to Etorofu.
"We have judged it would be important to report the current state of the (disputed territories) during Russian Prime Minister Vladimir Putin's visit to Japan. As we had no other choice, we obtained permission from Russian authorities," the broadcaster said.
Putin began his three-day visit to Japan on Monday.
The islands of Etorofu, Kunashiri and Shikotan, as well as the Habomai islet group, were seized by Soviet forces at the end of World War II.