Russia warned the West on Friday against sending troops to Ukraine to buttress its ally, after Kiev accused Moscow of building up a military presence on its border. Ukrainian President Volodymyr Zelensky on Thursday accused Russia of massing troops on the border and the United States pledged to stand by Ukraine in the event of Russian "aggression". Weeks of renewed frontline clashes have raised fears of an escalation of the simmering conflict in eastern Ukraine, where government forces are battling pro-Russian separatists. Speaking to reporters on Friday, Kremlin spokesman Dmitry Peskov said Russia would be forced to respond if the...