Former Russian President Dmitry Medvedev called Saturday on Japanese Prime Minister Fumio Kishida to die by "seppuku," a ritualistic suicide by disembowelment, after he and U.S. President Joe Biden warned Russia against using a nuclear weapon in Ukraine.

The deputy chairman of Russia's Security Council called a joint statement in which the Japanese and U.S. leaders made the warning a "horrible shame" and said he would not "even comment on the paranoia regarding our state's nuclear plans," Tass news agency reported, citing his Telegram channel.

File photo shows then Russian Prime Minister Dmitry Medvedev on Etorofu Island, one of the four Russia-held islands off Hokkaido that are claimed by Japan, on Aug. 2, 2019. (Kyodo)

Kishida can only "wash off" his shame by disemboweling himself at a meeting of his Cabinet ministers, Medvedev said, adding that the prime minister ignored that the United States is the only country to use nuclear weapons and Japan its victim.

In the statement issued after their meeting in Washington on Friday, Kishida and Biden said, "We state unequivocally that any use of a nuclear weapon by Russia in Ukraine would be an act of hostility against humanity and unjustifiable in any way."

They also said they are firmly opposed to Russia's "unjust and brutal war of aggression against Ukraine," adding that Japan and the United States will continue imposing sanctions on Moscow and provide "unwavering support" for Kyiv.

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