By Natalia Zinets and Pavel Polityuk KYIV (Reuters) – Ukrainian and Russian troops fought street by street for control of the industrial city of Sievierodonetsk on Monday in a pivotal battle of the Kremlin offensive in Ukraine’s eastern Donbas region. Which side had the upper hand was unclear, with “the situation changing from hour to hour”, the Ukrainian governor of Luhansk province, which forms part of the Donbas, said in a Telegram post on Monday evening. Sievierodonetsk has become the main target of the Russian offensive in the Donbas – comprising Luhansk and Donetsk provinces – as the Kre…