TOKYO (Kyodo) -- A close aide to Russian President Vladimir Putin visited one of several Russian-held, Japan-claimed islands earlier this month for a vacation, a source in Russian's Sakhalin region said Saturday.

Sergei Kiriyenko, first deputy chief of staff of the Presidential Executive Office, made the visit to Etorofu Island, off Japan's northernmost main island of Hokkaido, in a personal capacity, the source said, marking an unusual move for a high-ranking Russian official.

It is unclear whether Kiriyenko's visit was linked to a potential visit by Putin to any of the disputed islands, which are called the Northern Territories by Japan and the Southern Kurils by Russia.

Although Putin expressed such an interest in January, he said in June that no concrete plans were in place.

Kiriyenko initially visited Shumshu Island in the northeastern part of the Kuril Islands with Russian Deputy Prime Minister Yury Trutnev and Sakhalin Gov. Valery Limarenko on Oct. 10, according to a release by the regional government.

He then traveled to Etorofu with Limarenko but acted independently of him, avoiding the accommodation typically used by high-ranking officials and instead opting to stay in a guesthouse in the central town of Nayoka until Oct. 13, the source said.

Despite the Japanese government maintaining that visits to the disputed islands by Russian officials are "unacceptable," they have continued intermittently, including a visit by Trutnev to Etorofu in July.

Shumshu Island was the scene of several days of intense fighting that began on Aug. 18, 1945, between Soviet forces and the Japanese troops who were still in the process of demobilizing after Japan's unconditional surrender to the Allied Powers in World War II on Aug. 15 of that year.

Russia plans to establish an outdoor museum on the island to commemorate the 80th anniversary of its victory next year. Kiriyenko has said he would report the results of his inspection to Putin.