An extremist group claimed on a Web site posted Monday that it has killed an American taken hostage in Iraq and issued a video showing a man being shot in the back of the head.

The Islamic Army of Iraq claimed Ronald Allen Schulz, an American adviser, had been killed.

The video did not show the face of the victim, however, and it was impossible to identify him conclusively. The victim was kneeling with his back to the camera, with his hands tied behind his back and blindfolded with an Arab headdress when he was shot.

The videotaped killing showed the man being shot as he kneeled in an open, empty area of dirt. The video also showed Schulz's identity card.

In a separate piece of film, shown on a split screen as the killing was aired, the extremist group also showed a picture of Schulz alive. The group had aired the same footage of Schulz alive when he was first taken hostage earlier this month.

The group first claimed to have killed Schulz in an Internet posting last week. It had said then that it would show the killing.

Schulz, a civilian contractor, has been identified by the extremist group as a security consultant for the Iraqi Housing Ministry, although neighbors and family from Alaska, where he lives, say he is an industrial electrician who has worked on contracts around the world.

Schulz, a native of North Dakota, served in the Marine Corps from 1984 to 1991. He moved to Alaska six years ago, and friends and family say he is divorced.