Russian Prime Minister Dmitry Medvedev on Friday made his first visit since 2015 to one of the four Russia-held islands off Hokkaido that are claimed by Japan, despite a request by Tokyo to cancel the trip.

Japan protested the Russian premier's trip to Etorofu Island, called Iturup by Russia, with Chief Cabinet Secretary Yoshihide Suga saying the visit "conflicts with our country's stance on the territorial dispute."

It is Medvedev's fourth visit to one of the disputed islands. Japan claims the Northern Territories, known as the Southern Kurils in Russia, were illegally seized by the Soviet Union following Tokyo's surrender in World War II.

Tass news agency said Medvedev was not worried about the Japanese protest. "It is our land, it is an entity of the Russian Federation. These islands are part of the Sakhalin Region. Why should we be concerned about it?" the prime minister was quoted as telling reporters on the island.

"The more indignation (it causes), the more reasons to come here for Russian government representatives, and that's what we will do, of course," said Medvedev.

Medvedev inspected the construction site of a local school and residential buildings on the island and also visited a seafood processing factory and a hot spring facility, according to the report.

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With bilateral negotiations on the isles row remaining stalled, the Russian prime minister's visit is believed to be intended to highlight Moscow's control of the island through its efforts to develop the remote territory.

Japanese Prime Minister Shinzo Abe plans to meet Russian President Vladimir Putin in the eastern Russian city of Vladivostok next month on the sidelines of an economic conference. Japan has been promoting the programs in its bid to secure their eventual return.

In November 2010, as Russia's then-president, Medvedev visited Kunashiri, another of the four islands, becoming the first Russian leader to visit one of the contested islands.

He visited Kunashiri again in July 2012 as prime minister and Etorofu in August 2015.

Each visit has prompted a formal protest from Japan, and bilateral relations were particularly strained after he told Kunashiri residents in 2012 that Moscow would never return the islands.

(Photo taken Jan. 30, 2019, from a Kyodo News airplane shows Russian-held, Japanese-claimed islands off Japan's northernmost main island of Hokkaido.)

Etorofu is the most developed of the four disputed islands. Russian entity Gidrostroy, a major fishery and infrastructure company in the region, has created jobs there through its projects.

With the deployment of new surface-to-ship missiles onto the island in 2016, Etorofu is also seeing Russian military buildup.

The territorial dispute has prevented Russia and Japan from concluding a postwar peace treaty.

In November 2018, Abe and Putin agreed to step up talks on a peace treaty based on a 1956 joint declaration between the two countries which mentions handing back to Japan two areas -- Shikotan Island and the Habomai islet group.

But further progress has yet to materialize, with Putin apparently concerned that his waning popularity may decline further if he hands over the two islands.