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 His prophet."

A statement posted with the picture suggested the group was holding other soldiers.

"Our mujahadeen heroes of Iraq's Jihadi Battalion were able to capture American military man John Adam after killing a number of his comrades and capturing the rest," said the statement, signed by the "Mujahedeen Brigades."

"God willing, we will behead him if our female and male prisoners are not released from U.S. prisons within the maximum period of 72 hours from the time this statement has been released," the statement said.

The claim, carried on the Web site ansarnet.ws, could not be verified.