Boats dock at the port of Kurilsk in December 2016. (Archive photo: AFP/VNA)

Tokyo earlier this month called a visit by Russian Prime Minister Dmitry Medvedev to one of four islands claimed by both Japan and Russia extremely regrettable. Japan calls the islands the Northern Territories, while Russia calls them the Southern Kuril.

The Russian foreign ministry said Japan’s comments about what Russia did on its sovereign territory were unacceptable. It said it had also handed Japan’s ambassador a note of protest over what it said were violations of a visa-free exchange regime related to the disputed islands.