Moscow reacted angrily on Thursday to Washington's possible involvement in the Russian-Japanese territorial dispute over to the Kuril Islands.

The reaction came in response to recent U.S.-Japanese consultations at the level of foreign and defense ministers who agreed to facilitate the normalization of Russian-Japanese relations by resolving the issue of "the Northern Territories."

Both Japan and Russia have laid claims to the South Kuril Islands, called the Northern Territories by the Japanese, since they were annexed by the Soviet Union at the end of World War II. The dispute has prevented the two countries from signing a peace treaty to formally end hostilities.

Russia's Foreign Ministry said U.S. interference in the dispute was "inappropriate."

"Questioning Russia's sovereignty over the South Kuril Islands, which are part of Russia's territory as a result of World War II, as enshrined in the UN Charter, is inappropriate," the ministry said in a statement.

The long-standing territorial dispute escalated last November following Russian President Dmitry Medvedev's visit to one of the four South Kuril Islands. Japanese Prime Minister Naoto Kan called Medvedev's trip "inexcusable rudeness," sparking an angry reaction from the Kremlin.