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.

Crew of the U.S. Coast Guard cutter Stratton witnessed the Russian military vessels cross the maritime boundary and venture 30 miles inside an area extending beyond U.S. territorial waters known as the U.S. Exclusive Economic Zone, the Coast Guard said in a news release.

…

There have been several similar encounters in recent months. Last month, a U.S. Coast Guard cutter on routine patrol around Alaska’s Aleutian Islands came across a Russian ship in international waters but within the U.S. exclusive economic zone.

On July 6, the Coast Guard while on patrol spotted four Chinese military ships north of the Amchitka Pass in the Aleutian Islands in international waters, but also within the U.S. exclusive economic zone, officials said.

And on July 24, the U.S. military intercepted two Russian bombers and two Chinese bombers flying together in the Alaska Air Defense Identification Zone. The bombers were intercepted by U.S. and Canadian fighter jets and were not seen as a threat, according to North American Aerospace Defense Command.