"One marine assigned to First Marine Expeditionary Force was killed in action June 26 in the Al-Anbar Province while conducting security and stability operations," said a coalition statement, without providing further details.

Another statement said a marine, identified as Corporal Wassef Ali Hassoun of Lebanese descent, operating west of the flashpoint town of Fallujah, had been missing since June 21 but could not confirm that he was being held hostage.

"Contrary to press reports... Naval Criminal Investigative Services can not confirm that Corporal Wassef Ali Hassoun has been taken hostage," it said.

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

It identified the US hostage as Hassoun Wassef Ali, claiming to have abducted him after "infiltrating a US military base in Iraq," but gave no deadline for carrying out their grisly threat.

The group said the marine would be beheaded unless "all Iraqi detainees in the prisons of the occupation forces are released".

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

Separately, another Arab television channel, Al-Arabiya showed four hooded gunmen standing behind a man who was described as a Pakistani employee and threatened to behead him within 72 hours unless Iraqi prisoners are released.

A member of the group, reading a statement, said they captured the Pakistani who worked at a US base in Balad, 75 kilometres (45 miles) north of Baghdad.

The ID of the Pakistani was shown, naming him as Yussef Amjid, an employee of US contractor Kellogg Brown and Root (KBR).

The Pakistani government was unable to confirm whether one of its nationals had been abducted and no one at KBR was immediately available for comment.

Meanwhile a group of armed militants threatened Saturday to kill three Turkish hostages unless Ankara pulls its companies out of Iraq within 72 hours, in a videotape also broadcast on Al-Jazeera television.

South Korean hostage Kim Sun-Il was beheaded last Tuesday by his abductors who claimed the attack in the name of an al-Qaeda-linked group. And US national Nicolas Berg was beheaded in May.

In early April a US soldier identified as Private Keith Maupin, was captured by guerrillas and remains missing with no word on his fate.

Al-Jazeera had also broadcast video footage purported to be of Maupin.

Since April, a wave of kidnapping has swept Iraq, targetting foreign nationals working with the US-led coalition and on reconstruction projects.

WAR.WIRE