Russian President Vladimir Putin visited the far-eastern Kuril Islands for the first time on Thursday, prompting strong protests from Japan, which also claims the territory.

The islands, known in Japan as the Northern Territories, were seized by the Soviet Union in 1945 and have long strained relations between the two countries.

The Kremlin released a video of Putin on one of the four main islands, where Russian media reported he inspected a fish-processing plant and was presented with caviar. Japanese Prime Minister Sanae Takaichi described the visit as offensive to the Japanese people and “absolutely unacceptable.”

Takaichi said the Northern Territories remain an inherent part of Japan under both history and international law. She added that the visit would make it more difficult to restore relations between the two nations in the medium to long term.

Putin travelled to the Kurils after a stop on nearby Sakhalin Island, where Russia’s navy was conducting drills.

Ties between Japan and Russia have worsened since the full-scale conflict in Ukraine began, with Japan joining other G7 countries in imposing sanctions on Moscow.

The contested islands form part of a volcanic chain stretching from Russia’s Kamchatka peninsula to Japan’s Hokkaido. About 20,000 Russian citizens live there in a harsh climate, while the islands hold mineral deposits and rich fishing grounds. Japan continues to demand their return.

Photo credit: Belsat In English