Today is Japan's Northern Territory Day, marking the anniversary of an 1855 Japan-Russia friendship treaty that gave Japan possession of the islands. The Soviet Union seized the islands near the end of World War II -- a move Japan says was illegal.
Tokyo and Moscow have had diplomatic ties since 1956, but the island dispute has kept them from signing a postwar peace treaty.
The islands are part of a chain running from Japan's northernmost island, Hokkaido, to Russia's eastern Kamchatka Peninsula.
About 17,000 people, nearly all Russians, live on the islands.