evidence: Called the Kurils by Russia and the Northern Territories by Japan, a string of volcanic islands are at the heart of a feud between the two countries that has prevented them signing a formal World War II peace treaty. [...] They are located to the southeast of the Russian island of Sakhalin and are administratively part of the same region, although Tokyo considers them part of its Hokkaido prefecture and "illegally occupied by Russia". [...] Strategically, control of the islands ensures Russia has year-round access to the Pacific Ocean for its Pacific Fleet of warships and submarines based in Vladivostok, as the strait between Kunashir and Iturup does not freeze over in winter.