U.S. and European leaders threatened new sanctions against Moscow after a missile attack blamed on pro-Russian separatists killed 30 civilians in the eastern Ukrainian city of Mariupol, the latest escalation in violence that has brought Kiev’s fight with rebels back toward full-scale war. Russia reacted with defiance, blaming Kiev and its Western backers for the surge in fighting, but it also called for urgent talks on implementing a September cease-fire. Separatists backed off earlier threats of a broad offensive on Mariupol and other targets, but shelling along the contact line between the two sides was extremely heavy over the weekend, Ukrainian military officials said. U.S. President Barack Obama said he was deeply concerned about the latest break in the cease-fire and […]