SIVERS’K, Ukraine—Crammed into a damp cellar under a former hospital nicknamed “the sanctuary,” Katia stirs water and potato chunks in a plastic bucket as the vibrations of not-so-distant artillery strikes permeate the shelter. With little water and no power for more than a year, the frail pensioner has struggled to stay alive, living underground in Sivers’k, about 10 kilometres from the front line near Bakhmut, the city in eastern Ukraine where Russian forces are close to victory after months of fierce fighting. “Do you know how long we will have to live in the cellar?” she asked the Star reporters...