The US has accused Russia of building up its largest military presence along its border with Ukraine since October 2014. Air defense systems have also been deployed, the US says.
Russia's War Against Ukraine
Deutsche Welle: US accuses Russia of building up military presence in Ukraine
Pro-Russian separatist soldiers stand on their tank as they drive along a road near the village of Kirovske on April 21, 2015 in the self-proclaimed Donetsk People's Republic.
