An Al Qaeda cell fulfilled its threat to kill an American hostage, beheading him and showing the grisly photos on the Internet. Hours later, Saudi officials claimed they gunned down the militant who allegedly masterminded Paul M. Johnson's (search) kidnapping.

But a Web posting that appeared Saturday denied Abdulaziz al-Moqrin (search), the reputed leader of Al Qaeda (search) in Saudi Arabia, was killed. Officials had said he was slain in a firefight after police tracked down the car that dumped Johnson's body just outside Riyadh Friday.

"Some satellite networks and news agencies have been propagating the false news that Abdulaziz al-Moqrin, God preserve him, has been killed," the statement said, using a different spelling of his name. "We would like to say that such claims, unleashed by the tyrants of Saudi Arabia, are aimed at dissuading the holy warriors and crushing their spirits."

The statement's authenticity was impossible to verify, but it appeared on a Web site that has had similar messages in the past. A U.S. official who spoke on condition of anonymity Friday had confirmed al-Moqrin's killing, while a Saudi official had said forensic tests would confirm its identity.

Johnson, who had worked in Saudi Arabia for more than a decade, was the latest victim of an escalating campaign of violence against Westerners that aims to drive foreign workers from the kingdom and undermine the ruling royal family, hated by Al Qaeda. Usama bin Laden, Al Qaeda's leader, is a Saudi exile.

Johnson's severed head was shown on a Web site Friday. The photographs and a statement, in the name of Fallujah Brigade of Al Qaeda in the Arabian Peninsula (search), appeared after Johnson's wife went on Arab television and tearfully pleaded for his release.

"In answer to what we promised ... to kill the hostage Paul Marshall (Johnson) after the period is over ... the infidel got his fair treatment," the Al Qaeda statement said. "Let him taste something of what Muslims have long tasted from Apache helicopter fire and missiles."

President Bush condemned the beheading and vowed that "America will not be intimidated by these kinds of extremist thugs."

After news of Johnson's death was released, a Saudi security official said a witness took note of the license number of a car from which his body had been dumped just outside Riyadh Friday and informed police. Police stopped the car at a gas station in central Riyadh and a shootout ensued in which al-Moqrin was killed along with two other militants, Saudi officials said.

Three security officials were killed and two wounded. A security official in Riyadh said Rakan Mohsen Mohammed Al Saykhan, the second most-wanted Saudi militant, was wounded in the clash and arrested.

The statement denying al-Moqrin's death was signed by al-Moqrin's group and it said another message wound appear soon.

The killing of al-Moqrin, 31, would be a coup for the Saudi government, which has been under intense pressure to halt a wave of attacks against Westerners in the kingdom.

Johnson, 49, who worked on Apache attack helicopter systems for Lockheed Martin, was kidnapped last weekend by militants who threatened to kill him by Friday if the kingdom did not release its Al Qaeda prisoners. The Saudi government rejected the demands.

One of three photographs posted on the Web site showed a man's head, face toward the camera, being held by a hand. The two others showed a beheaded body lying prone on a bed, with the severed head placed in the small of his back, the clothes underneath bloodied. One showed a bloody knife resting on the face.

The beheaded body was dressed in a bright orange jumpsuit, similar to one Johnson is seen wearing in earlier videos released by the kidnappers.

"To the Americans and whoever is their ally in the infidel and criminal world and their allies in the war against Islam, this action is punishment to them and a lesson for them to know that whoever steps foot in our country, this decisive action will be his fate," the Al Qaeda statement said.

There are 35,000 Americans among the millions of Westerners who work in Saudi Arabia.

Soon after the statement appeared, a number of Web sites that had links to it became inaccessible, with messages saying they were closed for maintenance.

Johnson's beheading is the latest in a new, more dramatic wave of terror attacks for Saudi Arabia: bodies dragged on streets, traffic police blown up in their offices, hotel guests taken hostage and a chef shot outside an ATM machine. The attacks have killed dozens of people, mostly foreigners, over the past two months.

The violence is escalating despite an aggressive campaign by the government to root out terrorism, leaving many wondering whether the attacks are just the beginning or -- as the government continues to insist -- the last gasps of a desperate group reacting to the pressure of the hunt.

Johnson was seized on June 12, the same day that Islamic militants shot and killed Kenneth Scroggs of Laconia, New Hampshire, in his garage in Riyadh.

Scroggs worked for Advanced Electronics Co., a Saudi firm whose Web site lists Lockheed Martin among its customers. The office number on Johnson's business card was for Advanced Electronics.

The same week as Scroggs' death, militants shot and killed another American, Robert Jacobs, and Irish citizen Simon Cumbers in Riyadh.

A video released by the same militants showed attackers bent over Jacobs body, making a sawing motion near the head. But there was no confirmation that he had been decapitated.

Earlier, as the deadline approached, Johnson's Thai wife, Thanom, made an appearance on Al-Arabiya.

"When I see his picture in TV, I fall down," Thanom said, fighting back tears. "When I hear the name Paul Johnson, I cry a lot."

After Johnson's death was reported, his family in the United States was in seclusion at a home in Galloway Township, New Jersey, where they had been holding a vigil.