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By Pavel Polityuk and Kiryl Sukhotski KIEV (Reuters) - Russian troops are strengthening their positions in eastern Ukraine and using aid shipments to smuggle in arms and other supplies to separatist forces, Kiev's military said on Tuesday. Military spokesman Andriy Lysenko said units of Russian troops had been identified in the big regional center of Donetsk, towns and villages to its east and in south-east areas near the Sea of Azov. Fifteen more Ukrainian servicemen were killed in fighting in the past 24 hours, Lysenko said. President Petro Poroshenko accused Russia on Monday of "direct and undisguised aggression" in Kiev's five-month war against pro-Russian separatists.