By Alessandra Prentice and Natalia Zinets KYIV (Reuters) -Ukrainian soldiers resisted a Russian ultimatum to lay down arms on Sunday in the pulverised port of Mariupol, which Moscow said its forces had almost completely seized in what would be its biggest prize of the nearly two-month war. Ukrainian Prime Minister Denys Shmyhal said troops in Mariupol were still fighting despite a Russian demand to surrender by dawn. “The city still has not fallen,” he told ABC’s “This Week” programme, adding that Ukrainian soldiers continue to control some parts of the southeastern Ukrainian city. Russia said…