The U.S. Coast Guard said Monday that it tracked a group of Russian naval vessels, including two submarines, as they crossed into U.S. waters off Alaska in an apparent effort to avoid sea ice, a move that is permitted under international rules and customs.

The Chukchi Sea is the one that bounds the United States. It is in the north of the Bering Strait, a waterway separating Russia's Chukchi Peninsula to the west and Alaska to the east, connecting the Pacific Ocean to the south and the Arctic Ocean to the north.

The U.S. military has moved more than 100 soldiers along with mobile rocket launchers to a desolate island in the Aleutian chain of western Alaska amid a recent increase in Russian military planes and vessels approaching American territory.

Eight Russian military planes and four navy vessels, including two submarines, have come close to Alaska in the past week.

The US moved hundreds of soldiers and mobile rockets launchers to Shemya island in Alaska's Aleutian chain amid an increase in Russian military activity.