Russia's Foreign Ministry says it has lodged a protest with Tokyo for marking four Russian islands as Japanese territories in materials used at the G20 summit in Osaka.
Russia controls the four islands. Japan claims them.
Ministry spokesperson Maria Zakharova said the protest was made on Tuesday through the Japanese Embassy in Moscow.
Speaking on Thursday, she said Russia told Japan that Tokyo abused its role as G20 chair to advance its unfounded territorial claims to the islands.
The materials criticized by Russia are believed to include a video with a map of Japan showing the islands in the same color as the country's main territory.
The Japanese Embassy told NHK it doesn't accept the protest and that it explained Tokyo's stance to Russia.
The Japanese government maintains the islands are an inherent part of Japan's territory. It says the islands were illegally occupied after World War Two.
But Russia's latest protest shows it wants Japan to recognize that the islands became Russian territories as a result of the war.
Japanese Prime Minister Shinzo Abe met Russian President Vladimir Putin in Japan on June 29.
They agreed to promote bilateral negotiations toward a peace treaty based on a 1956 joint declaration. The declaration states that Russia will hand over two of the four islands after a peace treaty is concluded.