Japan protested Monday against a visit by Russian First Deputy Prime Minister Igor Shuvalov to two of the four Russian-held islands also claimed by Japan, Kyodo News agency reported.

Japanese Prime Minister Naoto Kan expressed his strong disappointment over the visit, saying "it is very regrettable" that Shuvalov visited the disputed islands.

Kan said that Japan's Vice Foreign Minister Kenichiro Sasae has already conveyed Tokyo's protest over the visit to Russian Ambassador to Japan Mikhail Bely, according to Kyodo report.

Shuvalov toured Kunashiri and Etorofu islands to inspect infrastructure earlier in the day, Itar-Tass news agency reported, despite Tokyo's criticism of President Dmitry Medvedev's previous visit to Kunashiri -- the first by a Russian leader to any of the islands the Soviet Union seized at the end of World War II.

Medvedev's visit on Nov. 1 made him the first leader from Russia or the former Soviet Union to set foot on any of the islands, which are called the Northern Territories in Japan and the Southern Kurils in Russia.