The U.S. and its allies are waiting for Vladimir Putin's next move.
As Russian forces tighten their hold on the Crimean Peninsula, the next few days will be crucial.
Both the Russian and Ukrainian forces are poised to react to the slightest provocation.
More than 100 unarmed Ukrainian soldiers tried to return to a Ukrainian military base north of Sevastopol Tuesday morning when about a dozen Russian soldiers fired warning shots over their heads.
Video shot by one of the Ukrainian soldiers showed the Ukrainians continuing to move forward. In the video, a Russian, holding his weapon, orders them to halt their advance: "I have orders; I will shoot you in the legs if you come any further."
Just how powerful is the Russian military?
CNN's Barbara Starr has a detailed look Putin's forces.