Former Russian prime minister Dmitry Medvedev has stressed that his country will refuse to negotiate a handover of territory with Japan under the new Russian constitution.
Medvedev, who now serves as the deputy head of Russia's Security Council, made an online appearance on Wednesday at a youth forum in Sakhalin in Russia's Far East.
Medvedev cited Russia's new constitution, which bans the cession of territory or any deliberations on such matters except for the demarcation of borders.
Russia controls the four islands of Habomai, Shikotan, Kunashiri and Etorofu. 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.
Tokyo and Moscow have yet to sign a peace treaty 75 years after the end of the war with the territorial issue left unresolved.
The Japanese government had criticized Russia's military parades on the islands of Kunashiri and Etorofu on Thursday, calling them unacceptable. The Japanese government says it aims to conclude a peace treaty by resolving the territorial issue.
Until last year, Russia marked the end of World War Two on September 2. But it changed the date this year to September 3, which was previously designated a national holiday to celebrate its victory over Japan.