Japan has lodged a protest through diplomatic routes with Russia over its planned firing drills in waters near the island of Etorofu. Japan claims the island as part of its Northern Territories.
Russia's government told Japan's Foreign Ministry on Monday that the drills will start on Wednesday and continue through Saturday.
Chief Cabinet Secretary Yoshihide Suga told reporters on Wednesday that the exercises could lead to a Russian military build-up on the 4 islands that include Etorofu.
Russia controls the islands. 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.
Suga said the planned Russian military drills are incompatible with Japan's position.
He said that to fundamentally solve such a problem, it's necessary to settle the territorial issue itself.
He added that the government will persistently continue negotiations with Russia based on its policy, settling the issue of the islands' sovereignty first, and will then sign a peace treaty.