Japan's Prime Minister Shinzo Abe. Photo: Kyodo/Reuters

Japan “strongly protested” yesterday against Russian military exercises on Pacific islands that it also claims and which have been at the root of strained relations between the two countries since the end of World War II.

The exercises on the disputed islands are a blow to Prime Minister Shinzo Abe’s efforts to court resource-rich Russia and keep the door open to dialogue, despite the Ukraine crisis.

Russia seized the islands from Japan in the waning days of the war and the ensuing dispute has prevented the neighbours from signing a formal peace treaty.

The islands are known as the Southern Kuriles in Russia and the Northern Territories in Japan.

“Carrying out these sort of exercises in the Northern Territories is totally unacceptable,” Abe told reporters.

Japan lodged a “strong protest” at the Russian Embassy in Tokyo, the Japanese Foreign Ministry said in a statement, calling the exercises “extremely regrettable”.

Carrying out these sort of exercises in the Northern Territories is totally unacceptable

Japan had already protested at the beginning of the military exercises but reiterated its objections yesterday.

Colonel Alexander Gordeyev, a spokesman for Russia’s Eastern Military District, told the Russian news agency Interfax on Tuesday that the exercises had begun, involving military units in the region deployed to the islands.

He said more than 1,000 troops, five Mi-8AMTSh attack helicopters and 100 other pieces of military hardware would be involved in the manoeuvres.

The exercises included Etorofu and Kunashiri islands, which Japan claims. It also claims Shikotan island and the Habomai islet group.

Russia is at odds with Western powers over what NATO says is its massing of military forces along the border with Ukraine for a possible invasion to boost pro-Russian separatists in the country’s east. Russia denies any such intent.

Abe, however, has made an effort to improve Japan’s ties with Russia a key part of his diplomacy.

His government treads a fine line by imposing sanctions on Russia in step with ally the United States, but keeps them lighter than those ordered by Washington in a bid to prevent significant damage to relations with Moscow.