CAIRO, Egypt - An Islamic Web site carried a videotape Wednesday that appeared to show militants in Iraq beheading a man identified as a CIA agent. The authenticity of the videotape could not be verified immediately. The Internet site, regarded as a clearing house for tapes and statements by Islamic extremist groups, displayed footage of eight militants surrounding a seated man who wore a sign around his neck bearing his photograph and the letters CIA along with the word "visitor." In a close-up, the footage showed a masked militant holding a large knife to the man's throat, the militant chopped...