President Bush has condemned the killing of American Paul Johnson by Islamic militants in Saudi Arabia. The body of the civilian engineer was found Friday in Riyadh, six days after his abduction. Mr. Bush, speaking in Seattle, said the United States will not be intimidated.

With confirmation of the engineer's death, Mr. Bush conveyed his "prayers and sympathies" to Mr. Johnson's family, and said the murder shows "the evil nature of the enemy."

"And it should remind us that we must pursue these people and bring them to justice before they hurt other Americans. See, they're trying to intimidate America. They're trying to shake our will. They're trying to get us to retreat from the world. America will not retreat," he said.

Mr. Johnson worked for the U.S. aerospace firm Lockheed Martin, which manufactures Apache helicopter gunships. He was abducted last Saturday in the Saudi capital.

A Saudi group loyal to Osama bin Laden posted pictures of the victim's severed head and body on several Islamic web sites.

His captors had imposed a Friday deadline for the release of militants held in Saudi prisons. Saudi forces had led an extensive search for the kidnappers, expanding it Friday to the farms and mountains outside Riyadh.

Mr. Johnson's death was the latest in a series of attacks on Westerners and other foreign workers in Saudi Arabia.

Democratic party presidential challenger John Kerry called the killing a "grotesque act."

Thursday, the State Department warned U.S. citizens living in the kingdom of serious threats to their safety, and repeated advice urging them to leave the country.

A Saudi spokesman in Washington said such calls to withdraw from his country "could inadvertently play into the hands of the terrorists."