Russian soldiers of Rapid Deployment Forces of the Central Asian nations take part on August 1, 2014 in joint military exercises 'Indestructible brotherhood - 2014' at the Ala-Too training ground, some 20 km outside Bishkek, the capital of Kyrgyzstan. The exercise gathers members of the Collective Security Treaty Organisation (CSTO), an intergovernmental military alliance which members are Russia, Belarus, Armenia, Kazakhstan, Kyrgyzstan and Tajikistan, that Moscow has touted to be a counterweight to the North Atlantic Treaty Organization (NATO). AFP PHOTO / VYACHESLAV OSELEDKO (Photo credit should read VYACHESLAV OSELEDKO/AFP/Getty Images)

MOSCOW, Aug 12 (Reuters) - Russia began military exercises in a Pacific island chain parts of which are also claimed by Japan, a Russian Defense Ministry spokesman said on Tuesday, a potential blow to Japanese Prime Minister Shinzo Abe's efforts to keep the door open to dialog with Moscow despite strains over the Ukraine crisis.

"Exercises began involving military units in the region, which are deploying to the Kurile Islands," Colonel Alexander Gordeyev, a spokesman for Russia's Eastern Military District, told the Russian news agency Interfax.

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

A Japanese foreign ministry official in Tokyo said the ministry was checking whether the exercises were taking part on islands that Japan considers its territory. The islands are known as the Southern Kuriles in Russia and the Northern Territories in Japan.

"If they are conducting a military exercise on the Northern Territories, we can by no means accept that in light of Japan's stance on the islands. We've already informed the Russian side of that stance and asked for clarification," the official said.

The dispute has strained relations Japan and Russia since the end of World War Two, when Soviet forces occupied the four islands at the southern end of the Kurile chain. The row has prevented the two countries from signing a formal peace treaty.

Russia is also 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. Moscow denies any such intent.

Abe, however, has made an effort to improve Japan's ties with resource-rich Russia one centerpiece of his diplomacy. His government has tread a fine line by imposing sanctions on Moscow in step with ally the United States but keeping them lighter than those ordered by Washington in an effort to keep relations with Russia from going into a deep chill.

(Reporting by Polina Devitt and writing by Alissa de Carbonnel in Moscow, with additional reporting by Linda Sieg and Kiyoshi Takenaka in Tokyo; Editing by Mark Heinrich and Robert Birsel)