relationship in syria, and it s up to the russians to explain what they re up to. reporter: mod ullr units have been installed. a defense official tells cnn, and this image broadcast on syrian state television, identified by analysts as a modern russian-made armored vehicle, not previously seen in syria, and painted in russian army camouflage. what the russians might or might not be doing at the moment, that s of concern to secretary kerry, and who would replace aassad? reporter: syria is russia s key alou. moscow also has a strategic naval base. if the fragile regime of bashiral assad falls, so too may russian influence in the region. russia and the united states had been talking about finding a political solution to the crisis. administration officials until recently expressing hope that moscow was open to a future without assad.