In another sign of potential friction in the warming Arctic, Canada has warned that it will step up patrols of the Northwest Passage.
Record summer melting of sea-ice has made the passage fully navigable; and immediately escalated a dispute over who controls the route.
Canada maintains that the waterway that connects the Atlantic with the Pacific lies within its territorial waters.
It has backed that up with plans for a new military base in the Arctic.
However, the United States, and other countries claim international rights to use the route for shipping
VIDEO: AT THE EDGE OF THE NORTHWEST PASSAGE