BAGHDAD, Iraq (AP) - Iraqi militants claimed in a Web statement Tuesday to have taken an American soldier hostage and threatened to behead him in 72 hours unless the Americans release Iraqi prisoners. The posting, on a Web site that frequently carried militants' statements, included a photo of what appeared to be an American soldier in desert fatigues seated with his hands tied behind his back. A gun barrel was pointed at his head, and he is seated in front of a black banner emblazoned with the Islamic profession of faith, "There is no god but God and Muhammad is...