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The Ukrainian president has been engaged in a frantic round of diplomatic activity in the past few days as Russia has markedly increased the number of troops deployed to the north and east of Ukraine and in occupied Crimea.

Russia’s purpose in the military buildup is unclear, but many western analysts are concerned about the scale of the posturing at a time of increased tensions between Moscow and Washington, after Joe Biden told reporters he thought his Russian counterpart, Vladimir Putin, was “a killer”.