Prime Minister Shinzo Abe left Tokyo for Moscow on Monday afternoon for talks with Russian President Vladimir Putin.
Before his departure, Abe told reporters that negotiations with Russia on signing a peace treaty have been an issue for over 70 years, and resolving it is not easy.
He expressed hope that he and Putin will open their minds and make as much progress as possible in discussions that would include a solution to the issue of the Russian-held islands that are known in Japan as the Northern Territoties.
Russia controls the four islands. Japan claims them. The Japanese government maintains the islands are an inherent part of Japan's territory. It says the islands were illegally occupied after World War Two.
The 25th summit between the two leaders is scheduled for Tuesday.
After Moscow, Abe will head for Switzerland to attend the annual meeting of the World Economic Forum in Davos, for the first time in five years.
He says he will convey Japan's positions on such global topics as creating rules for the digital era, promoting free trade, climate change and measures to tackle plastic waste in the ocean.
He also expressed hope that Japan will exercise leadership as the host of this year's Group of 20 summit, which will be held in Osaka, western Japan.