Disputed islands will likely be a focus of Japanese Foreign Minister Seiji Maehara's talks with his Russian counterpart in Moscow on Friday, ahead of which both sides have stepped up their rhetoric on sovereignty in the past days.

Tokyo's claim over the disputed islands remains "absolutely unwavering" despite Russia's decision to boost its military presence in the territory, Maehara told reporters on Thursday, hours before leaving for a four-day visit to Moscow.

Russian President Dmitry Medvedev said on Wednesday that Russia should deploy modern weaponry to ensure the security of the islands. He infuriated Japan in November by making the first visit by a Russian leader to one of the islands.

It is not wise for Tokyo to focus on the disputed islands if it wishes to improve ties with Moscow, which is unlikely to make concessions on this issue, experts said.

Relations between Japan and Russia have been clouded by a long-running dispute over the four islands, called the Southern Kurils by Russia and the Northern Territories by Japan.

The former Soviet Union occupied the islands off northern Japan at the end of World War II and the row has weighed on bilateral ties since, preventing the two countries from signing a formal peace treaty despite growing economic ties.

"The Northern Territories are the inherent territories of Japan, and Russia's occupation has no legal basis under international law," said Maehara, who is scheduled to hold talks with his Russian counterpart Sergei Lavrov on Friday.

"Regardless of how many (Russian) senior officials go there and who goes there, and whether it increases or decreases its military presence, the legal value (of Russia's claim) does not change," he said.

"Our resolve remains absolutely unwavering," said Maehara, who will also co-chair a meeting of the Japan-Russia Intergovernmental Committee on Trade and Economic Issues after meeting Lavrov.

Feng Zhaokui, former deputy chief of the Institute of Japan Studies at the Chinese Academy of Social Sciences, said Tokyo should not step up its rhetoric in the dispute if it aims to improve ties with Russia - an important neighbor rich in energy resources.

"It will be hard to resolve the dispute in a short period of time. Instead, it will further stimulate nationalism in both nations, harming ties," Feng said.

"If Tokyo sticks to the dispute, in which Russia is unlikely to make concessions, things will only turn worse, " said Feng.

Russian news agency ITAR-Tass cited a Defense Ministry source as saying that some of the four Mistral assault ships that Russia has contracted to buy from France would be deployed in the Pacific Fleet, in part to defend the Southern Kurils.

Japanese Chief Cabinet Secretary Yukio Edano responded on Thursday by saying that Japan is closely watching Russian military activity in the region.

Maehara can expect a frosty welcome when he visits Russia, for which he has only himself to blame and his own government to thank, said the English Web edition of the Asahi Shimbun, a major newspaper in Japan.

At a rally in Tokyo on Monday to call for the return of the Northern Territories, Japanese Prime Minister Naoto Kan referred to last November's visit to Kunashiri Island by Medvedev, calling it "an unforgivable outrage".

The Russian government was enraged by Kan's words, said Konstantin Sarkisov, head of the Center for Japan and Northeast Asia Diplomatic Academy in Russia, in an interview with Kyodo News Agency.

Sarkisov noted that taking so many years to solve the dispute is due to the lack of political resolution from both sides.

If both sides continue to stick to their own principles and refuse to make any concession, the talks between the two foreign ministers will end with no progress, he warned.

In 1956, the Japan-Soviet Joint Declaration restored diplomatic ties between the two nations, but a formal peace deal remained out of reach because of the territorial dispute.