Nato is putting forces on standby and sending fighter jets and ships to eastern Europe, insisting the alliance will "always do what is necessary to protect and defend all our allies".
Britain has joined the US in withdrawing some staff from the embassy in Kyiv, amid fears that Russia is poised to invade – which Moscow still denies, accusing the West of provocation.
With troops massed along the Russian side of the border – and neighbouring Belarus taking part in war games with Moscow
We visited the city of Mariupol in the Donetsk region, 15 miles from the border with the pro-Russian separatists.
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