On Tuesday, Moscow planned to begin military exercises off of Japan’s mainland despite the Tokyo Olympics. The island was seized by Japan in 1945 and Tokyo still claims authority over the land. Russia’s prime minister allegedly visited islands in the same disputed group just a day before the incident. Government spokesman Katsunobu Kato stated that Japan would not accept Russia’s moves to strengthen its military in the territories. The tension comes amid the Tokyo Olympics, which Russia has been banned from competing in. Russian athletes currently compete under the name Russian Olympic Committee due to a state-sponsored doping program that was exposed several years ago.

The military exercises will run until late August, says Russia. Russia also allegedly held military exercises in the island grouping in June. Tension over the islands has increased as Japan takes a firmer stance towards the dispute. Russia and Japan have not formally signed a peace treaty marking the end of hostilities following a declaration of war called by the Soviet Union on Japan during the final few days of WWII. After Russian Prime Minister Mikhail Mishustin’s visit to the disputed islands, he claimed that the government is considering setting up a special economic zone in the region in which businesses and investors would be free of taxes and customs duties.

Read More: Russia Holds Military Drills Off Japan’s Mainland During Tokyo Olympics