The United States' military presence in Japan has always been a stumbling block in Moscow and Tokyo reaching a peace treaty, the Kremlin said on Monday.
Japanese Prime Minister Fumio Kishida is due to hold a summit in Washington this week with U.S. President Joe Biden, the first state visit by a Japanese leader in nine years.
The meeting is meant to showcase their close security and economic ties, with the two leaders expected to discuss cooperation on defence equipment and a possible upgrade in the U.S. military command structure in Japan.
"The de facto defence alliance is already there and we know about the United States' military potential that is stationed in Japan - by the way, close to our borders," Kremlin spokesman Dmitry Peskov told reporters.
"This has always been a stumbling block in trying to reach a settlement of our main problem, the peace treaty problem."
Russia, the main successor state to the Soviet Union, and Japan have never signed a peace treaty formally ending their hostilities during World War Two.
A territorial dispute over a disputed Pacific island chain, known in Russia as the Kurils and in Japan as the Northern Territories, is a key issue.
Former Russian President Dmitry Medvedev said in January that Japan would have to drop territorial claims to the islands if it wanted to conclude a peace treaty.
Moscow withdrew from peace treaty talks with Japan and froze joint economic projects related to the islands in 2022 because of Japanese sanctions over Russia's war in Ukraine. Relations have soured further since.
