Moscow insists that the four tiny volcanic islands just off the northern tip of Hokkaido are rightfully Russian territory, endorsed by wartime agreements between the Allies at Yalta and Potsdam. But Tokyo argues that, unlike other post WW II territorial transfers, the legal case with the Kuril Islands remains murky and subject to further negotiation.
Most experts say the fate of the Kurils is the single reason Japan and Russia have failed to sign a formal peace treaty in the 65 years since the war ended, and there is no more certain way to stoke national passions in both countries than by raising the issue.
So why did Medvedev, returning to Moscow from a state visit to Vietnam, go several thousand miles out of his way to spend a morning on a barren rock that the Russians call Kunashir Island, the closest of the four to Japan?
"Medvedev wants to show the people of Siberia and the far east that he cares about them, and aims to develop these lands," says Yevgeny Bazhanov, vice rector of the Foreign Ministry's Diplomatic Academy in Moscow, which trains Russian diplomats.
"But it's also a signal to the Japanese that this is our land, and if they want to discuss that, they need to sit down at the table and talk with us," he says. "There have been no negotiations. The Japanese behave as though they won World War II, and that's not the way to go about it."