The Arctic could be a key avenue for Russian cruise missiles, and the military must engage in the region to protect against it, according to a top U.S. general.

Most of the discussion on missile defense is centered on traditional ballistic missiles or the advanced hypersonic missiles currently being developed by major powers, according to Air Force Gen. Terrence O'Shaughnessy, commander of U.S. Northern Command.

"But surprisingly there's not that much conversation about cruise missiles. And when I look at the cruise missile threat, I see that as one of the biggest threats that we face," O'Shaughnessy said during a Monday talk at the Center for Security and International Studies in Washington, D.C.

"If you look at the northern approaches through the Arctic, that's a key avenue of approach that we have to be able to defend."

Warmer temperatures in the Arctic have opened up potential sea lanes for both trade and military purposes, and Russia has wasted no time in taking advantage of the situation. The Russian military has built new and upgraded bases in the region over the last several years for its Northern Fleet. Last month, the Russian military tested the new surface-to-air missile system, which it plans to deploy to the Arctic. In September, the Northern Fleet tested its Bastion missile system, which reportedly is designed to engage large ships, including aircraft carriers.

O'Shaughnessy also pointed to Russia's cruise missile-carrying submarines as a potential threat emanating from the Arctic region.

"We haven't trained up there to the level that we probably should have over the last several decades," he said.

The military appears to have caught on to the importance of the Arctic region to some extent. Soldiers, Marines, sailors, and members of the Coast Guard have all engaged in increased Arctic training and exercises over the last two years. Last month, U.S. Marines in Norway participated in Thunder Reindeer 19, an annual live-fire exercise designed to prepare for combat in the Arctic area.