Japan's foreign minister warned Russia on Wednesday not to make any provocative moves over four Russian-held islands that both nations claim.
Foreign Minister Taro Aso told Japan's parliament that Tokyo had filed a request through Russia's Foreign Ministry urging Moscow to avoid "any provocative actions" following last weekend's visit to the islands visit by Russian Foreign Minister Sergey Lavrov.
Aso did not elaborate. His remarks came amid renewed speculation the two countries may soon discuss the islands' fate.
Russia captured the four islands at the southern end of the Kuril chain - which Japan calls the Northern Territories - from Japan near the end of World War II.
Tokyo has demanded that Moscow cede to Japan all four islands, surrounded by rich fishing grounds. The dispute has kept the two countries from signing a peace treaty formally ending their World War II hostilities.
Japanese Prime Minister Shinzo Abe and Russian President Vladimir Putin are due to meet, and it is believed that they may discuss the issue on the sidelines of a summit of the Group of Eight industrialized nations in Germany this week.
On Monday, Putin said Moscow is ready to work with Tokyo on a solution.
"This situation arose as a result of World War II and has been formalized in international law, in international documents," Putin said.
"We understand the motives of our Japanese partners' behavior. We would like to get rid of all the thorns of the past, and together with Japan we are looking for a solution to this issue," Putin said.
More than 3,500 people were detained during unprecedented mass protests that swept across all of Russia in support of Alexey Navalny on January 23