Russia promises retaliation against US for Ukraine strike on Crimea ReutersRussia tells US ambassador it will retaliate over Sevastopol missile strike Al Jazeera EnglishRussia summons the American ambassador over a deadly attack that Moscow says used US-made missiles The Associated PressRussia threatens ‘consequences’ for US over Crimea missile strikes POLITICO EuropeRussia placing military near civilians in Crimea, to deter attacks: ISW Business Insider