Nato's military commander in Europe has issued a warning about the build-up of Russian forces on Ukraine's border. Supreme Allied Commander Europe Gen Philip Breedlove said Nato was in particular concerned about the threat to Moldova's Trans-Dniester region. Russia said its forces complied with international agreements. The build-up has been allied with Russia's annexation of Crimea from Ukraine, following the removal of Ukraine's pro-Moscow president. Moscow formally annexed Crimea after the predominantly ethic-Russian region held a referendum which backed joining the Russian Federation.