Russian President Dmitry Medvedev has visited an island chain claimed by Moscow and Tokyo, sparking sharp criticism from Japan. He is the first Russian president to visit one of the disputed Kurile Islands.
Russia and Japan each claim the four islands known as Southern Kuriles in Russia and the Northern Territories in Japan. The Soviet Union seized the islands after declaring war on Japan at the end of World War II, forcing more than 15,000 Japanese residents to flee the area.
The territorial dispute prohibited the two countries from signing a formal peace treaty.
Mr. Medvedev said he visited the islands because he was interested in seeing how residents on the southernmost isle of Kunashir live.
He says, he wants to make sure that the leading social standards, on the islands, coincide with Russian standards throughout the country and that it is important that there are specialists and doctors in the area.
If the Kurile Islands were returned to Japan, the country would gain rich fishing grounds. The area is close to oil and gas regions in Russia. The islands stretch from Russia's Kamchatka Peninsula to about 15 kilometers from Japan's northern island of Hokkaido.
Japan's Prime Minister Naoto Kan was not happy with Mr. Medvedev's visit.
He says Japan has been consistent in its stance that the four northern islands are Japanese territory. He says he thinks it is regrettable that the president decided to visit the area.
Japanese Chief Cabinet Secretary Yoshito Sengoku says Japan will monitor Russia's actions and comments in regard to the unwelcomed visit.
He says it is necessary for Japan to see exactly what sort of comments Russia and the government make, and to decide upon an appropriate response.
Meanwhile, Russian Foreign Minister Sergei Lavrov lashed out at Japan's reaction to Mr. Medvedev's visit.
He says the reaction from the Japanese on President Medvedev's visit to the Kurile Islands was unacceptable. He says it is Russia's land.
Mr. Medvedev is to visit Japan this month for the Asia-Pacific Economic Cooperation leaders' summit.