By Alan Charlish and Hedy Beloucif WARSAW (Reuters) – A U.S. citizen who says he was held captive and beaten by Russian forces in Ukraine before being rescued by a private volunteer group spoke of his relief at reaching safety in Poland, describing his ordeal as an example of war crimes. Kirillo Alexandrov, 27, crossed the Polish border in the early hours of Wednesday and had an emotional reunion with his mother, who had contacted Florida-based nonprofit organisation Project Dynamo in the hope they could rescue her son. “Once we crossed the Polish border… a thousand-pound boulder just fell o…