By Maria Tsvetkova KYIV/MOSCOW (Reuters) -President Vladimir Putin put Russia’s nuclear deterrent on high alert on Sunday in the face of a barrage of Western reprisals for his war on Ukraine, which said it had repelled Russian ground forces attacking its biggest cities. The United States said Putin was escalating the war in a “totally unacceptable” way, amid signs that the biggest assault on a European state since World War Two was not producing rapid battlefield victories, but instead generating a far-reaching and concerted Western response. The Ukrainian president’s office said negotiations …