The United States must be more assertive in the Arctic region due to threats from China and Russia, the U.S. Navy said in a strategic plan revealed this week.

The 28-page "Blue Arctic: a Strategic Plan for the Arctic," released on Tuesday, is a blueprint of strategic guidance stressing integration with allies.

It notes that global warming is turning the Arctic region from ice-covered, or "white," to navigable, or "blue," and acknowledges the increasing maritime activity of China and Russia in the region.

"Russia is investing heavily to enhance its Arctic defense and economic sectors, with a resultant multilayered militarization of its northern flank," the document reads.

"By modernizing its military capabilities and posture, particularly the Northern Fleet, Russia aims to improve command and control, infrastructure, and joint force employment to project power and defend its northern approaches," it says.

Russia has reopened mothballed military bases in the region and operates a large fleet of icebreaker vessels, while China, which is not geographically extending to the Arctic Circle, is increasing its shipbuilding and port infrastructure, it says.

The plan notes that the Arctic is a strategic region of growing geopolitical and global importance, and holds an estimated 30% of the world's undiscovered natural gas reserves, 13% of the global conventional oil reserves and one trillion dollars' worth of rare earth minerals.

"Without sustained American naval presence and partnerships in the Arctic region, peace and prosperity will be increasingly challenged by Russia and China," the document says.

It adds that the Navy will also increase military training in the region.