By Jonathan Landay FRONTLINE NORTH OF KHERSON, Ukraine (Reuters) -Ukrainian President Volodymyr Zelenskiy urged the West to warn Russia not to blow up a dam that would flood a swath of southern Ukraine, as his forces prepared to push Moscow’s troops from the occupied city of Kherson. In a television address, Zelenskiy said Russian forces had planted explosives inside the huge Nova Kakhovka dam, which holds back an enormous reservoir, and were planning to blow it up. “Now everyone in the world must act powerfully and quickly to prevent a new Russian terrorist attack. Destroying the dam would me…