NATO's secretary general said on Tuesday that events in eastern Ukraine were cause for great concern and called on Russia to pull back troops from the border with its neighbour, Reuters reported. "Events in eastern Ukraine are a great concern, I urge Russia to step back," Anders Fogh Rasmussen told a NATO conference in Paris. "Any further move to eastern Ukraine would represent a serious escalation rather than de-escalation." He added that Russia had to pull back the "tens of thousands of troops" that had massed on Ukraine's borders.