MONS, Belgium—The U.S. has too few intelligence assets focused on the threat from Russia and should concentrate its technical capabilities on Moscow’s growing military might, NATO’s departing supreme allied commander said.

The U.S. has begun to build up the number of intelligence analysts examining Russia, which stood at 13,000 at the height of the Cold War before dipping to a low point of just 1,000 three years ago, said Gen. Philip Breedlove, the top military commander of the North Atlantic Treaty Organization, in an interview.

But Gen. Breedlove said the U.S. needs more technical intelligence assets, the kind of spy satellites the U.S. uses to keep an eye on both troop movements and terrorist training camps, focused on the threat from Russia.

“We see that Russia has not accepted the hand of partnership but has chosen a path of belligerence,” Gen. Breedlove said. “We need to readdress where we’re heading.”

Gen. Breedlove will step down this month after three years in the top military job at NATO, a time in which he has overseen the transformation of the alliance from one focused on expeditionary capabilities, like in Afghanistan, to the defense of Europe in the face of renewed aggression from Russia.