BRUSSELS—The European Union moved to dampen the latest diplomatic row with Moscow, with a spokeswoman for the bloc saying that Russian President Vladimir Putin's reported comments about sending forces into Kiev were "made public out of context."

Italian newspaper La Repubblica was the first to report that European Commission President José Manuel Barroso had told fellow leaders at Saturday's EU summit in Brussels that Mr. Putin had warned him in a telephone call the previous day Russian forces could take Kiev within...