Russia’s Ministry of Foreign Affairs has issued a formal diplomatic protest to Japan after accusing Tokyo of circulating a map at its G20 summit showing a disputed island chain as Japanese territory, the ministry’s spokeswoman said on Thursday.

The islands — known as the Northern Territories in Japan and the Southern Kuriles in Russia — have been controlled by Russia since the end of World War II and are the main reason the countries have not yet formally ended hostilities.

Japan hosted the Group of 20 summit in Osaka last month.

Maria Zakharova, the foreign ministry spokeswoman, said a note of diplomatic protest had been handed to a Japanese diplomat in Moscow on July 2.