Russia and Japan on Monday maintained their seemingly irreconcilable positions over their ownership claims to parts of the Kuril Islands volcanic archipelago in the north Pacific that Moscow has administered since the end of the Second World War (1939-45), amid tense negotiations.

Japan claims sovereignty to three islands and a group of islets that form part of the Kuril Islands' southernmost points located close to the northern tip of Hokkaido, but Russia has so far stood firm on its jurisdiction claims to the territories, which were annexed by the Soviet Union in the final says of the war 1945 in a move that Moscow says was justified by an international treaty six years later.

"We have called the attention of our Japanese friends to the fact that the sovereignty of these islands is not up for discussion: it is territory of the Russian Federations," Sergei Lavrov, Russia's foreign minister, said, adding that he told his Japanese counterpart, Taro Kono, it was unacceptable for Japan to keep referring to the islands in question as its Northern Territories.

The islands, which have an area of 10,502 square kilometers (4,005 square miles) stretch from northern Japan to the southern tip of Russia's Kamchatka, separating the Sea of Okhotsk and the Pacific Ocean.

Japan's foreign minister gave a limited press statement regarding the discussions in Moscow.

"Both parties exchanged opinions and expressed their point of view. It was a serious conversation," he said.

Russia's President Vladimir Putin and Japanese Prime Minister Shinzo Abe are due to meet in Russia on Jan. 22.

Tokyo claims sovereignty over Iturup island, Kunashir, Shikotan and the Habomai islands.

In 1951, the Allied Powers and Japan signed the San Francisco Treaty, which saw Tokyo renounce its claim to the South Kuril Islands, although the text did not ratify the USSR's sovereignty over the territory.

The territorial dispute re-emerged when Japan and the Soviet Union normalized ties.

Several Western institutions, such as the European Union, have postured in favor of Russia handing the islands back to Japan.

Moscow has so far rejected this stance.