NATO's chief says the economic crisis could threaten the national security of members of the military alliance, and he's urging them to maintain defense spending to close gaps in their military capabilities.

Secretary-General Anders Fogh Rasmussen told reporters in Brussels that "our security rests on our prosperity: you can't be safe if you're broke. But in turn, our prosperity rests on our security."

One concern in NATO's annual report is the impact of national austerity measures on defense capabilities within the alliance. Total defense spending by NATO members is dropping while that of emerging powers is rising.

Fogh Rasmussen says "if these trends continue, we could face serious gaps that would place NATO's military capacity and political credibility at risk."