The Russian Foreign Ministry shrugged off on Monday Japanese discontent over a Russian state visit to the disputed Kuril Islands.

"We remind you that Russia's sovereignty over these islands has indisputable international and legal foundations," the Russian Foreign Ministry told RIA Novosti. "So 'regrets' regarding the Russian officials' visit to the islands are inappropriate."

The Russian delegation led by Deputy Prime Minister Sergei Ivanov visited the Kunashir and Iturup islands on Sunday as part of a working tour around Russia's Far East.

The Japanese Foreign Ministry lodged an official complaint with the Russian embassy in Tokyo on Monday.

Both Japan and Russia have laid claims to the South Kuril Islands, called the Northern Territories by the Japanese, since they were annexed by the Soviet Union at the end of World War II. The dispute has prevented the two countries from signing a peace treaty to formally end hostilities.

The long-standing territorial dispute escalated in November last year following a visit by Russian President Dmitry Medvedev to one of the four South Kuril Islands. Japanese Prime Minister Naoto Kan called Medvedev's trip "inexcusable rudeness," sparking an angry reaction from the Kremlin.

MOSCOW, May 16 (RIA Novosti)