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of the army of Ansar al-Sunna, Abdallah Al-Hassan ben Mahmoud" to US President George W. Bush and demanded US forces be withdrawn from the country.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, a Muslim, 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 man with a mustache, dressed in camouflage garb, with a sword brandished over his head and close-ups of identification cards.

The group said it had abducted the missing Marine after "infiltrating a US military base in Iraq".

His family said he was a translator and had joined the marines almost two years ago after becoming a US citizen.

Ansar al-Sunna on Friday claimed responsibility for the killing of an Iraqi official the previous day in Baghdad and called on Iraqi soldiers to put down their weapons and no longer support the "renegade" government of Prime Minister Iyad Allawi.

Dozens of foreigners have been kidnapped in Iraq since April. Some have subsequently been released and others have been killed.

Insurgents have beheaded two hostages in the past two months: South Korean translator Kim Sun-Il and American contractor Nicholas Berg.

A Pakistani, Amjad Hafeez, who worked as a driver for an American company, was kidnapped last Sunday in Baghdad, but was released by his captors on Friday, according to his family.

Two Turkish hostages held by an armed group in Iraq were freed on Friday. Video footage released by their captors said they had pledged not to work for the "filthy" Americans again.

WAR.WIRE