TOKYO (Reuters) - Japan has conveyed its concern to Moscow over possible Russian plans to build a naval base on a western Pacific island chain, part of which are claimed by Tokyo, a top Japanese government spokesman said on Monday, the latest in a long-running territorial spat.
Tokyo's action follows Russian Defence Minister Sergei Shoigu's comment last week that Russia would study the possibility of building a naval base on what it calls the Kurile islands.
Japan claims a southern segment of the island chain, which was seized by Soviet troops at the end of World War Two. The territorial row has kept the two countries from signing a formal peace treaty since.
The disputed islands are called the Northern Territories in Japan and Southern Kuriles in Russia.
"We've informed the Russian side through a diplomatic channel that we are concerned about the comment by Defence Minister Shoigu," Chief Cabinet Secretary Yoshihide Suga told a regular news conference.
"We've also told them that if this led to the reinforcement of Russian military infrastructure on the Northern Territories, that would be incompatible with Japan's stance and regrettable."
Besides the potential construction of a naval base, Shoigu also said last week that Russia would this year deploy some of its newest missile defense systems and drones on the Kurile islands.
The military buildup in Russia's Far East comes when Japan is shifting its defense focus to the south to better cope with China's maritime expansion.
Japan on Monday switched on a radar station in the East China Sea, giving it a permanent intelligence gathering post close to a group of islands disputed by Japan and China, drawing an angry response from Beijing.
(Reporting by Kiyoshi Takenaka in Tokyo, Dmitry Solovyov in Moscow; Editing by Nick Macfie)