By Pavel Polityuk and Vladyslav Smilianets KYIV/SIVERSK, Ukraine (Reuters) -Russia has stepped up a “powerful assault” led by the Wagner contract militia on Soledar in eastern Ukraine, Kyiv said on Monday, describing a difficult situation for forces repelling waves of attacks around the salt mining town and nearby fronts. Soledar, in the industrial Donbas region, lies a few miles from Bakhmut, where troops from both sides have been taking heavy losses in some of the most intense trench warfare since Russia invaded Ukraine nearly 11 months ago. Ukrainian forces repelled an earlier attempt to ta…