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 U.S. military said it was investigating, but the claim's authenticity could not be immediately confirmed.

The posting, on a Web site that frequently carried militants' statements, included a photo of a man purported to be an American soldier, wearing desert fatigues and seated on a concrete floor with his hands tied behind his back.

A gun barrel was pointed at his head, and behind him on the wall is a black banner emblazoned with the Islamic profession of faith, "There is no god but God and Muhammad is His prophet."

A U.S. military spokesman in Baghdad, Marine Sgt. Salju K. Thomas, said he had no information on the claim but "we are currently looking into it."