Prime Minister Fumio Kishida said he told Ukrainian President Volodymyr Zelenskyy on Friday that Japan will never recognize Russia's annexation of parts of southern and eastern Ukraine, emphasizing it is an act that violates international law.
Kishida also told reporters after his telephone conversation with Zelenskyy that Japan will consider further sanctions on Russia and continue supporting Ukraine in efforts to end the war, launched by Moscow in February, as soon as possible.
Russian President Vladimir Putin on Friday declared the annexation of four occupied Ukrainian regions, in an escalation of his country's now seven-month-long war against its neighbor.
Voting in what Western officials say are sham referendums to be used as a pretext for Russian annexation took place in Zaporizhzhia and Kherson in the south as well as Donetsk and Luhansk in the east.
Ukraine has condemned the votes, while leaders of the Group of Seven industrialized nations issued a statement vowing they will also "never recognize" the referendums or an annexation.
Earlier Friday in Tokyo, Japan's Foreign Minister Yoshimasa Hayashi lambasted Russia, saying that Moscow's move "infringes on Ukraine's sovereignty."
Japan will "never overlook unilateral action that changes the status quo by force" and will work closely with the G-7 and the international community to support Ukraine, Hayashi told reporters.
Kishida and Zelenskyy talked over the phone for around 30 minutes in a call that was held at the request of Ukraine, a Japanese government official said.
The G-7 major developed nations have been ramping up pressure on Moscow, tightening economic sanctions against it and pledging to reduce their reliance on Russian energy resources. Russia launched cross-border military operations on Feb. 24.
Speaking to Japanese lawmakers by video link in March, Zelenskyy asked Japan to ban trade with Russia to stop what he called the "tsunami" of its invasion into Ukraine, as he stressed the need to ramp up sanctions to punish Moscow.
Russia's invasion of Ukraine has pushed up energy and food prices across the globe, which has created a drag on the economy of resource-poor Japan. Japan depends on imports for more than 90 percent of its energy needs.
As the yen's rapid depreciation has also driven up import costs while wages in Japan have remained stagnant, the Kishida administration has been urged to implement measures to ease the impacts of price hikes.
In the wake of Russia's invasion of Ukraine, relations between Tokyo and Moscow have deteriorated sharply.
In early September, Russia scrapped an agreement with Japan to allow visa-free visits by Japanese former residents of disputed islands off Hokkaido. Russia has criticized Japan for participating in Western sanctions against Moscow in response to the war in Ukraine.
The dispute over the islands -- Etorofu, Kunashiri, Shikotan and the Habomai islet group -- has prevented the two nations from signing a post-World War II peace treaty.
The row stems from the seizure of the territory by the Soviet Union, Russia's predecessor state, in the weeks following Japan's surrender on Aug. 15, 1945.
The G-7 is made up of Britain, Canada, France, Germany, Italy, Japan and the United States, plus the European Union.