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(CNN) – Russian troops have taken positions in Ukraine's Crimea peninsula, as world leaders scramble to find a solution to this conflict.
Now, moves at sea are also raising the stakes, in a key channel into the Black Sea, a Turkish waterway identified as a world oil transit choke point by the U.S. government.
The Bosphorus Strait was the scene of a tense situation involving a key Ukrainian warship that CNN's Ivan Watson was tailing off the coast of Turkey.