Russian President Vladimir Putin visited the disputed Kuril islands on Thursday, marking his first in-person visit to the territory. During the trip, Putin visited Etorofu, which is known in Russia as Iturup.
The Japanese government and the foreign minister issued strong protests in response to the visit. Tensions over the Russian-controlled archipelago, which is claimed partly by Japan, have long dogged bilateral ties.
The islands are located off the east coast of Japan's northernmost Hokkaido island. The territory was seized by the Soviet Union in 1945 and remains occupied by the former Soviet Union while being claimed by Japan.