Hundreds of Russians protested against a feared giveaway of strategic islands to Japan on Sunday, two days before a key summit between the countries' leaders in Moscow.
The Soviet army claimed four islands, the so-called south Kurils, in the closing days of World War II.
The dispute over their sovereignty prevented the two countries from signing a peace treaty, a situation President Vladimir Putin and Prime Minister Shinzo Abe sought to rectify last year.
Abe is set to hold talks on the issue with Putin on Tuesday, following a meeting last week between foreign ministers Sergei Lavrov and Taro Kono.
Moscow has said the islands' sovereignty is not a bargaining chip and the Kurils will remain Russian territory, but many people distrust official rhetoric and suspect a different line of negotiations behind the scenes.
Some protesters carried signs saying "The Kurils are Russian land" and "Giving away the Kurils is state treason", an AFP correspondent observed.
The Kremlin has ridden a wave of nationalism following Moscow's annexation of Crimea from Ukraine in 2014, and any attempt to structure an agreement with Japan around a territorial compromise would likely be poorly received.
Protester Svetlana Fedosova, 26, said ceding the islands would be seen as a "weakness" by Russia's enemies and would lead to Russia's undoing.
"Other countries will also demand re-addressing the results of World War II," she said.
"Then we'll have to give away Karelia, Kaliningrad, and all the lands we've conquered," she told AFP, referring to Russia's western regions that previously belonged to Finland and Germany.
"People demand a stop to backstage talks with Japan", one of the rally's organisers, leftist politician Sergei Udaltsov, wrote on Twitter after the rally.
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