Government forces started pulling out of a town in eastern Ukraine on Wednesday after a fierce assault by Russian-backed separatists which Europe said violated a crumbling ceasefire. President Petro Poroshenko said before flying to the town of Debaltseve that more than 80 percent of his troops in the rail hub had already left following a heavy bombardment and street-by-street fighting despite the truce that took effect on Sunday. Rebels say the ceasefire, negotiated by Ukraine, Russia, Germany and France at a summit in Belarus last week, does not apply to Debaltseve, which links the two rebel-controlled regions of eastern Ukraine, Donetsk and Luhansk. Poroshenko and the West say the rebel assault is being reinforced by Russian tanks, artillery and soldiers, though Moscow denies sending forces to join the battle for a region that President Vladimir Putin has called "New Russia".