In the Ukrainian city of Izyum, the country's blue and yellow flag has just been raised again over the charred city hall, months after Russian tanks barrelled in.

Gleeful residents rush to a hill near a cell phone tower, the only place in town with a signal, to call relatives to share their good news: the Russians are out.

Ukrainian soldiers liberated the eastern city at the weekend as the army reclaimed swathes of territory, part of its rapid counter-offensive to beat back Russian soldiers who invaded February 24.