TOKYO (Reuters) - Russian President Vladimir Putin arrived in Japan on Thursday for talks with Prime Minister Shinzo Abe aimed at improving ties, but both sides have scaled back expectations of major progress towards a peace treaty formally ending World War Two.
Blocking the treaty is a territorial row involving four islands off Japan's northern island of Hokkaido that were seized by the Soviet Union at the end of World War Two.
Following are some key facts about the islands.
The islands, known as the Northern Territories in Japan and the Southern Kuriles in Russia, are called Kunashiri, Etorofu, Shikotan and the Habomai group of islets in Japanese. They are known in Russian as Kunashir, Iturup, Shikotan and Habomai.
The islands were home to about 17,000 Japanese people, who fished, bred horses and mined gold, among other occupations, before they were seized by the Soviet Union after it declared war on Japan in the closing days of World War Two. The inhabitants were forced to flee.
The current population is 12,346, according to the Russian government.
The disputed islands form the southern end of the Kurile Island chain that stretches for 1,250 km (780 miles) from the southern tip of Russia's Kamchatka Peninshula to Japan's northern main island of Hokkaido, dividing the Sea of Okhotsk to the west and the Pacific Ocean to the east.
Their total land area is almost 5,000 square km (2,000 square miles), according to Japan's Foreign Ministry - a little smaller than the U.S. state of Delaware and less than half the size of Lebanon. On clear days, Kunashiri is visible from Hokkaido.
Most inhabitants depend on fishing for their livelihoods and Japan would gain rich fishing grounds if it regained full control of the islands, partly through extending its exclusive economic zone.
The islands are close to oil- and gas-producing regions of Russia, and may themselves harbour rich mineral deposits, a tempting possibility for resource-poor Japan. But upgrading the island infrastructure to match that of the rest of Japan would be expensive.
They have strategic value for Russia as a sea lane to the Western Pacific for their navy.
In 2011, as many as 3,500 Russian troops belonging to the 18th Machine Gun-Artillery Division were deployed on the islands, said a top official in the Russian General Staff, quoted by Russian news agency Interfax.
The unit is reinforced with self-propelled artillery, anti-aircraft systems, rocket artillery and seven dozen tanks, the Russian Defense Ministry broadcaster Zvezda said.
Russian Defence Minister Sergei Shoigu said in March Russia would study the possibility of building a naval base in the islands, prompting protests from Japan.
In November, Russian media reported that Bastion and Bal anti-ship missile systems were in operation on the islands. Japanese Prime Minister Shinzo Abe called that development "regrettable".
Addition reporting by Denis Dyomkin; Editing by Robert Birsel and Christian Schmollinger