Russia has rejected Japan's protest over its 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 4 days of drills will 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. He said the Russian military drills are incompatible with Japan's position.
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.
A statement issued by Russia's Foreign Ministry on Wednesday says that the country is sovereign and can act however it wants in its territory, including ways to strengthen national security.
The statement criticized Japan's protest as being unhelpful in regard to forming a positive atmosphere in the bilateral relationship, and that it could cause diplomatic damage.
It added that any concerns which arise should be handled not by ritual protests, but through the existing mechanism of dialogue between the two countries.