A previously unknown militant group claimed responsibility on a militant Web site for the slaying of a U.S. diplomat in Sudan on New Year's Day, according to an intelligence group monitoring extremist groups. "We can't authenticate this communique, which is posted by a member of the forum, but at the same time, because there is a claim of responsibility, we chose to send it out to our subscribers," Rita Katz told The Associated Press. Katz is the director of monitoring institute, SITE Intelligence Group. Katz added that she had never heard of the group before. The group calls itself Ansar...