Ukraine's second largest city, Kharkiv, is believed to have been one of the invading Russian military's first strategic targets. Home to 1.4 million people, it is located less than 20 miles from the Russian border, in northeast Ukraine. [Source]
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The build-up of Russian forces close to the Ukrainian border continues apace, with everything from submarines and amphibious landing ships in the Black Sea to short-range ballistic missiles, tanks and howitzers around Ukraine's northeastern edges.