Russia shifts tactics, steps up pace of assault in Ukraine's east and south

The war in eastern Ukraine appears to be entering a critical phase, as Russia pours in more fighting units and Ukrainian forces try to hold lines battered by weeks of shelling and rocket fire.

On Wednesday, the Ukrainian military acknowledged losing territory in two different areas of the long front lines they are defending, a reflection perhaps of the sheer volume of Russian forces being deployed as well as improving Russian tactics.

Essentially Ukrainian forces are defending three sides of a slowly shrinking pocket in the east, with their only supply lines running in from the west. The risk -- if the Russians make progress -- is that some of the Ukrainian army's best units, lacking protection from the air, could be cut off.