Russian President Vladimir Putin made his first visit Thursday to a group of Russian-held islands off the east coast of Hokkaido that are claimed by Japan, sparking strong pushback by Tokyo.

The Russian leader visited Etorofu, the largest and northernmost of the four disputed islands known in Japan as the Northern Territories that have been occupied by Russia since the end of World War II. The others are Kunashiri, Shikotan and Habomai.

The visit comes at a time of year when Japan and the world look back on the atomic bombings of Hiroshima and Nagasaki, Saturday¡¯s anniversary of the end of WWII, and the subsequent Soviet Union invasion of the northern islands.