The Foreign Ministry said it summoned the U.S. ambassador to a meeting on Monday to register disapproval of American support for Tokyo in a territorial dispute over a group of Pacific islands.
In a meeting with Ambassador John Beyrle, Deputy Foreign Minister Alexei Borodavkin repeated Moscow's claim of sovereignty over the southern Kuril islands, the ministry said.
Moscow and Tokyo both claim the four small, windswept islands off Japan's Hokkaido that Soviet forces occupied at the end of World War II. Japan calls them the Northern Territories.
The dispute has prevented the nations from signing a peace treaty, and tension has escalated since November, when President Dmitry Medvedev became the first Russian leader to visit the islands.
The Russian Foreign Ministry said Beyrle was summoned because of recent statements by U.S. diplomats "in which support was expressed for Japanese territorial claims against Russia."
A U.S. Embassy spokesperson said there had been no change in the longstanding position of the United States, which supports Japan's claim but urges Russia and Japan to seek a peaceful resolution of the dispute.
Medvedev has said Russia will upgrade military units on the islands, and a visit to Moscow by Japan's foreign minister last week brought the sides no closer to a resolution.
