Russia will deploy extra weapons on a chain of Pacific islands that Japan also claims as its own.
The dispute between Moscow and Tokyo over the Southern Kurile Islands goes back to the end of World War II when they were seized by Soviet troops.
Russian President Dmitry Medvedev said: “Everyone must understand these islands belong to Russia. We will deploy sufficient force to strengthen our presence there. This is our strategic policy.”
Last November, Medvedev became the first Russian leader to set foot on the four islands, which are known in Japan as the Northern Territories.
The islands are surrounded by offshore reserves of oil and gas, as well as rich fishing grounds.
The Russian government hopes to attract tourists to the islands and plans to invest 450 million euros there by 2015.