Hundreds of U.S. troops are headed for maneuvers in Eastern Europe through year’s end, the Pentagon announced, new deployments intended to reassure allies on Russia’s borders as violence took a sinister turn Tuesday in embattled Ukraine. Vice President Joe Biden, in a visit to Kiev, warned Russia to pull back its troops and abide by last week’s international agreement or face the certainty of swift new sanctions. Mr. Biden also urged Ukraine’s leaders to adhere to democratic principles and respect cultural differences, reassuring them, “You will not walk this road alone.” Despite Washington’s efforts, tensions flared as Kiev accused pro-Russian separatists of torturing and killing two people and of shooting at one of its military planes, prompting a call by the country’s interim president for a resumption of what he termed counterterrorism actions to uproot militants. More