"Right now he's captured. No one should be speculating" about his fate, US marine Lieutenant Colonel T.V. Johnson told AFP.

Johnson was responding to a message posted on an al-Qaeda linked website by the group Ansar al-Sunna that the Islamic militant group had beheaded Corporal Wassef Ali Hassoun.

The group also said it was holding another "infidel" hostage without specifying a nationality or the circumstances of the kidnapping.

"We inform you that the decapitation was carried out of a soldier with the marines, of Lebanese origin, (Wassef Ali) Hassoun and you will soon see the video," said the message posted on at least two Islamic websites.

The statement was addressed from the "emir of the army of Ansar al-Sunna, Abdallah Al-Hassan ben Mahmoud" to US President George W. Bush and demanded US forces be withdrawn from the country.

The statement said the US marine had "romantic relations with a young Arab girl and was lured away from his base."

Hassoun went missing June 21 near the flashpoint town of Fallujah, west of Baghdad. The US military had confirmed he was missing.

The Arab news channel Al-Jazeera broadcast a tape last Sunday from a group calling itself the "Islamic Retaliation Movement - Armed Resistance Wing," which said it had abducted a marine and would decapitate him unless all detainees in US-led military prisons were freed.

The tape showed a blindfolded, mustached man, dressed in camouflage garb, with a sword brandished over his head and close-ups of identification cards.

WAR.WIRE