By Pavel Polityuk and Oleksandr Kozhukhar KYIV/LVIV (Reuters) – A Moscow backed separatist leader was reported by state-run TASS news agency on Tuesday as saying that Russian forces had not advanced as rapidly as they had hoped in the battle for Sievierodonetsk, the easternmost city still in Ukraine’s hands. As the Russian offensive continued across Ukraine’s eastern Donbas region, the European Union agreed to ban most imports of Russian oil, a move intended to blow a hole in the Kremlin’s war finances. In the bloc’s toughest sanction on Moscow since the invasion of Ukraine three months ago, E…