The leaders of Japan and Russia are holding talks in Argentina. They are expected to discuss a mechanism to speed up negotiations on a peace treaty.
Shinzo Abe and Vladimir Putin are meeting on the sidelines of the G20 summit. Abe is hoping to reach an agreement on the mechanism.
Last month, Abe and Putin agreed to accelerate the negotiations, based on the 1956 joint declaration.
It says Moscow will hand over to Japan 2 of 4 Russian-held islands after the conclusion of a peace treaty. A treaty was never signed after World War Two.
The stumbling block has been a territorial dispute over the 4 Russian-controlled islands. Japan claims them.
Its government maintains they are an inherent part of Japan's territory. It says they were illegally occupied after the war.
Russian officials have suggested Moscow may not automatically hand over the islands.
Its government has said long and complex discussions need to take place on the islands' sovereignty. Moscow has also said it wants to make sure American troops will not be deployed on them.
