Japan is protesting Russia’s decision to break off negotiations formally ending nearly eight decades of lingering hostilities from World War II because of Tokyo’s response over Russia’s invasion of Ukraine.

The two nations have been trying to reach a peace treaty for years to resolve a disputed chain of islands off Japan’s northern island of Hokkaido, known in Russia as the Kurils and the Northern Territories in Japan. The islands were seized by Russia, under the banner of the Soviet Union, at the end of World War II.

Japan has imposed a number of economic sanctions on Russia in reaction to the invasion, and has announced plans to revoke Russia’s most-favored nation trade status. Russia’s Foreign Ministry announced Monday it was ending the talks, accusing Tokyo of taking an unfriendly position against the country and trying to damage its interests.

But Japanese Prime Minister Fumio Kishida Tuesday said Russia is entirely to blame for the situation because of its invasion of Ukraine, and that the decision to break off talks “extremely unjustified” and “unacceptable.”

Chief Cabinet Secretary Hirokazu Matsuno said Monday it has lodged an official protest with Russia over dissolution of the talks.

Some information for this report came from The Associated Press, Reuters and Agence France-Presse.