BRUSSELS, March 23 - NATO's top military commander said on Sunday Russia had built up a "very sizeable" force on its border with Ukraine and Moscow may have a region in another ex-Soviet republic, Moldova, in its sights after annexing Crimea, Reuters reported.

Russia was acting more like an adversary than a partner, NATO's Supreme Allied Commander Europe, U.S. Air Force General Philip Breedlove said, and the 28-nation alliance should rethink the positioning and readiness of its forces in eastern Europe.