By Phil Stewart WASHINGTON (Reuters) – If Russia unleashes the forces it has amassed near Ukraine’s border to invade its neighbor, the outcome would be “horrific” and result in significant casualties, the top U.S. military officer said on Friday, comparing this moment to the Cold War. Army General Mark Milley, the chairman of the Joint Chiefs of Staff, made the comments amid fragile Russia-U.S. diplomacy in a broader East-West standoff over Ukraine. Moscow has demanded NATO pull back troops and weapons from Eastern Europe and bar Ukraine from ever joining the military alliance. Washington and …