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.

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

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.

Russian military planes and navy vessels, including two submarines, have come close to Alaska in the past week as Russia and China conducted joint drills.