"Those of the samurai who feel especially sad can end their life in a traditional Japanese way, by committing seppuku. If they dare, of course," he wrote on X (formerly Twitter). Seppuku, also called harakiri, is a form of ritualistic suicide, News Week reports.

His inflammatory message came after Japanese Prime Minister Fumio Kishida delivered a speech to his country's parliament earlier in the day about signing a peace treaty with Russia to formally end World War II.

The dispute over the Kuril Islands is one of the main reasons why Russia and Japan have never signed such a treaty. The islands, which Japan calls the Northern Territories, are located in the Pacific Ocean between Russia's Kamchatka Peninsula and the Japanese island of Hokkaido.

Soldiers from the Soviet Union seized four of the islands at the end of World War II, and the land has been claimed by both Russia and Japan ever since.

According to Kishida, Tokyo is "fully committed" to negotiating a peace treaty with Moscow, but Medvedev shut down the proposal unless Japan accepts the Kuril Islands as part of Russia.