TOKYO (Kyodo) -- Russian authorities confiscated satellite-based mobile phones from Japanese officials when they were entering a Russian-controlled disputed island, bringing a strong rebuke from Tokyo.
The authorities seized the phones on Sunday from Japanese officials and press at an airport on Kunashiri, one of the Russian-administered, Japan-claimed islets off Hokkaido's east coast, the Japanese Foreign Ministry said Monday.
The Japanese government claims Russia has no authority to do so on an island that Japan maintains is an inherent part of its territory.
Chief Cabinet Secretary Yoshihide Suga said at a press conference that Japan has lodged a protest with Russia, saying it was "extremely regrettable."
The officials and press were part of a group of former residents of Kunashiri and their families visiting their ancestors' graves there.
A total of 70 Japanese people went on a two-day tour to Kunashiri and Etorofu, another disputed islet, and returned to an airport on Hokkaido on Monday.
The two islands along with Shikotan and the Habomai islet group were seized by the former Soviet Union at the end of World War II in August 1945. The dispute over the islands remains a long-standing issue that has prevented Tokyo and Moscow from concluding a postwar peace treaty.
Japan is seeking to settle the issue by accelerating planned joint economic activities on the islets called the Northern Territories in Japan and the Southern Kurils in Russia, as Japanese Prime Minister Shinzo Abe and Russian President Vladimir Putin agreed in 2016 to start negotiations over the projects.
The tour marked the second trip by air after an agreement last year to reduce the burden on the aging former Japanese residents of the disputed islands.
Before that, there had only been trips by chartered ships to the islands.