The Aleutian Islands (; possibly from Chukchi aliat, "island") are a chain of 14 large volcanic islands and 55 smaller ones belonging to both the United States and Russia. They form part of the Aleutian Arc in the Northern Pacific Ocean, occupying an area of 6,821 sq mi (17,666 km²) and extending about westward from the Alaska Peninsula toward the Kamchatka Peninsula in Russia, and mark a dividing line between the Bering Sea to the north and the Pacific Ocean to the south. Crossing longitude 180°, at which point east and west longitude end, the archipelago contains both the westernmost part of the United States by longitude (Amatignak Island) and the easternmost by longitude (Semisopochnoi Island). The westernmost U.S. island in real terms, however, is Attu Island, west of which runs the International Date Line. While nearly all the archipelago is part of Alaska and is usually considered as being in the "Alaskan Bush", at the extreme western end, the small, geologically related Commander Islands belong to Russia.